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Corrosion costs the global economy an estimated 3 to 4% of GDP annually. For structural steel in infrastructure, marine environments, chemical processing plants, and industrial equipment, the dominant protective strategy is the organic coating — a layered system designed to slow the electrochemical reactions that convert iron to iron oxide. At the heart of every anti-corrosion coating formulation sits the corrosion inhibitor: the ingredient that actively interrupts this process rather than merely slowing electrolyte access to the metal surface.



Understanding how inhibitors work, which mechanism applies to which substrate and environment, and how the regulatory transition away from chromates is reshaping the available palette is essential for anyone specifying or formulating industrial protective coatings.



The Electrochemical Basis of Corrosion



Corrosion of steel is fundamentally an electrochemical process. In the presence of water and oxygen, anodic and cathodic sites form on the metal surface. At the anode, iron is oxidized: Fe → Fe²⁺ + 2e⁻. At the cathode, oxygen is reduced: O₂ + 2H₂O + 4e⁻ → 4OH⁻. The resulting ions react to form rust. Current flows between anode and cathode through the electrolyte (water with dissolved ions) and through the metal itself.



The Bureau of Reclamation review on corrosion inhibiting mechanisms in coatings — one of the most comprehensive technical surveys of anti-corrosion coating science — establishes that binders in organic coatings provide inherent barrier protection by limiting access of oxygen, water, and corrosive anions to the substrate. However, all organic binders are permeable to some degree, and corrosive species inevitably reach the metal surface over time. This is where pigment-level inhibition becomes critical: it must function at the interface, not just at the film surface.



Three Mechanisms of Inhibition



1. Barrier Mechanism



The simplest mechanism is physical exclusion — pigments and extenders that block the pathways through which water and ions diffuse to the metal surface. Lamellar pigments (micaceous iron oxide, aluminium flake, talc) orient parallel to the substrate and force diffusing species to travel a tortuous path through the binder matrix, substantially extending the time before corrosive agents reach the metal.



Research on pigment volume concentration (PVC) effects in epoxy primers confirms that the optimal PVC for lamellar pigments is formulation-dependent: wollastonite and zinc phosphate outperform talc in combined anticorrosion efficiency and adhesion, while talc leads on physical-mechanical properties alone. The critical PVC — above which barrier efficiency deteriorates due to air voids in the pigment packing — is a key formulation parameter.



A ScienceDirect review on advances in corrosion protection notes that while barrier protection is universally assumed to be the primary function of organic coatings, the evidence base for the pigment barrier contribution specifically is less robust than for active inhibition — reinforcing the case for multi-mechanism systems.



2. Active (Passivation) Mechanism



Active inhibition relies on sparingly soluble pigments releasing inhibitive ions when water penetrates the coating. These ions migrate to the metal surface and either form a thin passivating oxide layer (anodic inhibitors) or block the cathodic reaction sites.



Phosphate pigments are the most widely adopted chromate-free active inhibitors. Zinc phosphate, in particular, has three proposed inhibition pathways: direct phosphate ion passivation of the iron surface; formation of a zinc-iron complex at the interface; and binding of phosphate ions with components of the binder resin to form protective metal soaps. PMC research on zinc phosphate in waterborne acrylic coatings confirms that zinc phosphate addition inhibits the anodic corrosion process and enhances wet adhesion, reducing lateral diffusion of the corrosive medium at the coating-metal interface.



The PMC review on phosphate inhibition of steel reinforcement confirms the thermodynamic basis: phosphate ions promote ferrous phosphate precipitation, creating a barrier layer at the metal surface that is chemically stable across the pH range of 8–12. Zinc phosphate modifications — aluminium zinc phosphate, zinc molybdate phosphate, zinc silicophosphate — extend the base chemistry to address specific binder systems and service environments.



Molybdate pigments operate through a similar anodic passivation pathway but are more sensitive to binder choice. Technical literature on corrosion inhibiting mechanisms notes a specific risk: molybdates can accelerate premature binder ageing, leading to film embrittlement — a relevant trade-off in formulations targeting long service life.



3. Cathodic (Sacrificial) Mechanism



Sacrificial protection works by preferential oxidation of a more electronegative metal in electrical contact with the steel substrate. Zinc is the standard sacrificial pigment in industrial primers. When zinc particles are in contact with each other and with the steel, as established in ScienceDirect research on zinc-rich primer electrochemistry, the zinc acts as an anode and the steel as a cathode — the potential difference drives zinc dissolution rather than iron dissolution.



The three-coat system (zinc-rich primer / epoxy midcoat / polyurethane topcoat) is the dominant specification for structural steel bridges and heavy industrial structures. ScienceDirect research on zinc-rich primer durability shows that initial zinc activity depletes progressively, and the protection mechanism shifts over time from cathodic protection to barrier protection, as zinc corrosion products fill the primer pores.



A critical formulation variable is zinc loading. For effective galvanic coupling, zinc particles must form a percolating network through the binder — typically requiring pigment volume concentrations above 60% for organic zinc-rich primers. PMC research on graphene-modified zinc primers demonstrates that partial substitution of zinc dust with graphene nanosheets at reduced PVC can maintain galvanic action by improving electrical connectivity between zinc particles, reducing total zinc content without sacrificing cathodic protection performance.



The Regulatory Transition: Replacing Chromates



Hexavalent chromium (Cr(VI)) was the dominant corrosion inhibitor for aerospace, military, and high-performance industrial coatings for decades. Strontium chromate and zinc chromate provided exceptional, multi-mechanism protection: anodic passivation, self-healing through chromate ion migration to scratched areas, and broad substrate compatibility. Their toxicity and carcinogenicity ended that dominance.



Under REACH Regulation (EC) No 1907/2006, Cr(VI) compounds — including chromate pigments — are subject to authorisation requirements across the EU. Researches on chromate-free strategies for magnesium alloys notes that equivalent performance alternatives have only recently emerged, despite decades of research, reflecting the genuinely exceptional inhibitive chemistry of Cr(VI).



The current chromate-free palette for primer formulations includes:




Zinc phosphate and its modifications (aluminium zinc phosphate, zinc molybdate phosphate) — established workhorse replacement, well-characterised, lower performance ceiling than chromate in aggressive environments.



Calcium-modified silica — heavy-metal-free, non-toxic, ion-exchange mechanism similar to zeolites; reviewed in Wiley's Advances in Polymer Technology as an environmentally safe alternative with growing adoption.



Zeolite-based pigments — porous structure allows loading of inhibitor ions (Ce³⁺, La³⁺, vanadates) and controlled release triggered by corrosion onset; reviewed as promising replacements for phosphate inhibitors in contexts where phosphate content is also under reduction pressure.



Organic inhibitors (benzotriazole, 2-mercaptobenzothiazole) — form protective adsorption films directly on the metal surface through nitrogen or sulfur coordination. PMC research on modified epoxy coatings confirms benzotriazole (BTA) and 2-mercaptobenzothiazole (MBT) as non-toxic, cost-effective triazole-based inhibitors with demonstrated corrosion inhibition across multiple metals and media.




Formulation Considerations



Binder Selection



The inhibitor's function is inseparable from the binder system. The PMC review on polymer-based coatings for steel establishes epoxy resins as the dominant binder for industrial anti-corrosion primers, valued for their chemical resistance, adhesion to metal substrates, and compatibility with a wide range of inhibitive pigments. Polyurethane topcoats extend UV resistance and mechanical durability without contributing primary corrosion protection — that function remains with the primer.



The pigment-binder interaction is not passive. Zinc phosphate, as noted above, can react with binder components to form metal soaps that contribute to the passivating layer. Conversely, molybdate pigments can degrade certain binder systems through premature oxidation. Compatibility testing is non-negotiable in system development.



Measuring Inhibitor Performance



Electrochemical impedance spectroscopy (EIS) is the primary quantitative tool for evaluating corrosion inhibitor performance in coated systems. By measuring the impedance response across a range of frequencies during immersion in electrolyte, EIS tracks the progressive degradation of barrier properties as water and ions penetrate the coating. Researches demonstrates EIS monitoring over 1,000 hours of immersion, capturing the transition from intact barrier to active corrosion at defect sites.



EIS is complemented by:




Salt spray testing (ISO 9227 / ASTM B117) for comparative ranking under standardised aggressive conditions



Cyclic corrosion testing (ISO 11997) for automotive and outdoor applications requiring temperature and humidity cycling



Scribe assessment (ISO 4628) for evaluating under-film corrosion propagation from mechanical damage sites




Smart and Self-Healing Systems



The leading edge of anti-corrosion coating research concerns stimuli-responsive inhibitor release — systems where inhibitors remain encapsulated until a corrosion event triggers their release. PMC research on mesoporous alumina as inhibitor carrier demonstrates 50% improvement in corrosion resistance at scratch sites when BTA is loaded into alumina particles within an epoxy matrix, compared to BTA-free controls. The swelling of inhibitor from particles to exposed bare metal provides localised, on-demand protection at defect sites.



Cerium nitrate, dodecylamine, and 8-hydroxyquinoline have all been demonstrated as encapsulatable inhibitors in microencapsulation systems, with controlled release responding to pH shifts (corrosion raises local pH), mechanical disruption, or moisture ingress.



Application to Specific Markets



For general industrial and maintenance applications — structural steel, process equipment, onshore wind structures, bridges — the Safic-Alcan coatings ingredient catalogue covers the range of anti-corrosion pigments, epoxy curing agents, and functional additives relevant to primer and topcoat formulation.



For formulators operating across the coatings, inks, and construction sector more broadly, the Safic-Alcan coatings market page provides access to ingredient families — binders, pigments, rheology modifiers, surface additives — with the regulatory and technical support needed to navigate chromate replacements and VOC reduction targets simultaneously.



Summary



Corrosion inhibition in industrial coatings operates through three mechanistic routes — barrier, active passivation, and cathodic protection — which are most effective when deployed in combination across a multi-coat system. The regulatory transition from chromate to chromate-free inhibitors has matured significantly: zinc phosphate and its modifications remain the standard replacement, while calcium-modified silica, zeolite-based pigments, and organic inhibitor packages address applications where phosphate performance is insufficient.



Formulation decisions — inhibitor choice, PVC, binder compatibility — must be validated electrochemically, not assumed. The measurement tools (EIS, salt spray, cyclic corrosion testing) are well standardised. What is changing is the inhibitor palette: both the replacement of Cr(VI) chemistry and the emergence of encapsulated, smart-release systems are expanding what is technically achievable without the toxicological legacy of previous-generation inhibitors.


Corrosion Inhibitors in Industrial Coatings


Formulators looking to replace conventional petroleum-based emollients or volatile silicones increasingly turn to the same two molecules:&nbsp;squalane&nbsp;and&nbsp;hemisqualane. Both are derived from renewable&nbsp;feedstocks,&nbsp;both deliver exceptional skin feel, and both carry a body of dermatological evidence that most bio-based alternatives cannot match. Understanding what differentiates them — chemically, functionally, and from a sourcing standpoint — is essential before making a formulation or sourcing decision.&nbsp;



The Biological Starting Point: Squalene in Human Skin&nbsp;



The relevance of squalane to skin care is not incidental — it is structural. Its precursor, squalene (C₃₀H₅₀), is a triterpene that forms a significant fraction of human sebum.&nbsp;NIH research on epidermal surface lipids&nbsp;identifies&nbsp;it as one of the predominant non-polar lipids secreted by sebaceous glands alongside triglycerides and wax esters. More specifically,&nbsp;the PMC review on squalene biology&nbsp;quantifies squalene at approximately 13% of total sebum composition — making it the single largest peroxidable fraction in skin surface lipids.&nbsp;



Its functional role is protective.&nbsp;Research on skin surface lipids as environmental mediators&nbsp;demonstrates that squalene's presence in human sebum, which is absent in the sebum of non-human primates,&nbsp;likely represents&nbsp;an evolutionary adaptation: its capacity to neutralize reactive oxygen species generated by UV irradiation positions it as a natural endogenous antioxidant and indirect photoprotective agent.&nbsp;



The problem with squalene in topical formulations is chemical instability.&nbsp;The 2025 dermatological study on squalane in fibroblasts&nbsp;notes that squalene carries six double bonds and oxidizes readily upon exposure, limiting its shelf life and generating comedogenic peroxides in formulated products. Hydrogenation saturates those bonds, producing&nbsp;squalane&nbsp;(C₃₀H₆₂) — chemically inert, non-comedogenic, and stable under normal storage conditions.&nbsp;



From Shark to Sugarcane: The Sourcing Shift&nbsp;



For most of the twentieth century, commercial squalane was derived from shark liver oil, which can&nbsp;contain&nbsp;squalene at concentrations far exceeding those found in plant sources. This dependency raised serious sustainability and ethical concerns, given the volume of deep-water shark catch&nbsp;required&nbsp;to supply the cosmetic industry.&nbsp;



Two plant-derived routes have since become dominant:&nbsp;



Olive-derived squalane&nbsp;is produced by hydrogenating squalene extracted from olive oil deodorizer distillate, a by-product of olive refining. It carries ECOCERT credentials and is well&nbsp;established&nbsp;in European markets. However, the squalene content of olive oil is relatively modest —&nbsp;precision fermentation research&nbsp;notes that even amaranth oil, one of the richest botanical squalene sources,&nbsp;contains&nbsp;only around 5.9% of the compound.&nbsp;



Sugarcane-derived squalane, pioneered by Amyris, relies on precision fermentation. As&nbsp;described in&nbsp;Cosmetics &amp; Toiletries, the yeast&nbsp;Saccharomyces cerevisiae&nbsp;is programmed to convert sugar into β-farnesene, a sesquiterpene that then undergoes chemical conversion into squalane. The output is essentially&nbsp;odourless, highly pure (&gt;99% C₃₀ hydrocarbon), and consistent lot-to-lot — characteristics difficult to guarantee with plant extraction.&nbsp;Research on precision fermentation for cosmetics&nbsp;notes&nbsp;that engineered yeast strains have achieved squalane yields 3 to 115 times higher than wild-type organisms, making the process commercially scalable.&nbsp;



The PMC review on microbial squalene&nbsp;confirms that fermentation-derived squalane is functionally indistinguishable from shark-derived material, while supporting environmental sustainability and enabling vegan certification.&nbsp;



Skin Functionality: What the Evidence Shows&nbsp;



Skin Functionality: What the Evidence Shows&nbsp;



Squalane's biomimetic structure allows it to integrate into the stratum corneum lipid matrix without triggering immune response or disrupting the skin microbiome. Its low molecular polarity gives it rapid, non-greasy spread across the skin surface, making it suitable for a wide range of leave-on formulations.&nbsp;



The ScienceDirect study on squalane-based emulsions&nbsp;demonstrates that squalane enhances the skin penetration of co-formulated actives, increasing compound diffusion through the stratum corneum and improving interaction with deeper skin layers — a relevant property when squalane is used as a carrier phase for polyphenols, vitamins, or lipophilic active ingredients.&nbsp;



The 2025 study on UV protection and collagen biosynthesis&nbsp;published in PMC found that squalane protects human dermal fibroblasts from UV-induced inhibition of collagen synthesis, suggesting a functional role beyond simple&nbsp;emolliency.&nbsp;



Transepidermal&nbsp;Water Loss Reduction&nbsp;



The&nbsp;Polymers&nbsp;cyclic compression review&nbsp;aside, the strongest clinical signal for squalane&nbsp;remains&nbsp;its effect on skin hydration.&nbsp;A 2023 study published in&nbsp;CosmoDerma&nbsp;documented statistically&nbsp;significant TEWL reductions at 7, 14, and 28 days of daily application, with progressive improvement over time consistent with cumulative barrier strengthening rather than surface-level occlusion.&nbsp;



Hemisqualane: The Silicone Replacement&nbsp;



Hemisqualane&nbsp;(INCI:&nbsp;C13–C15&nbsp;Alkane) is structurally half the size of squalane — a 15-carbon branched hydrocarbon. It is produced via the same β-farnesene&nbsp;fermentation pathway developed by Amyris, but the chemical conversion stops earlier. The result is a lighter, more volatile molecule designed to replicate the sensory profile of cyclic silicones.&nbsp;



Why Silicone Replacement Is Now a Formulation Priority&nbsp;



The regulatory context makes this transition urgent.&nbsp;Commission Regulation (EU) 2024/1328&nbsp;extended restrictions under REACH Annex XVII to D4, D5 (cyclopentasiloxane), and D6 (cyclohexasiloxane). D5, formerly the most widely used volatile silicone in cosmetics, is now capped at 0.1% in rinse-off products and subject to expanding restrictions&nbsp;in&nbsp;leave-on applications. The environmental basis is clear:&nbsp;PMC research on cyclomethicone&nbsp;confirms that D5 does not biodegrade readily in aquatic systems,&nbsp;accumulates in&nbsp;fish liver tissue, and has been classified as a very persistent, very bioaccumulative (vPvB) substance by ECHA.&nbsp;



What&nbsp;Hemisqualane&nbsp;Delivers&nbsp;



Biocosmetics research published in PMC&nbsp;describes&nbsp;hemisqualane&nbsp;explicitly as "a sustainable and naturally derived alternative to&nbsp;cyclomethicone," produced via sugarcane fermentation and inherently biodegradable. It carries ECOCERT approval and USDA Certified Biobased Product designation.&nbsp;



In formulation,&nbsp;hemisqualane&nbsp;provides rapid&nbsp;spreadability, a silky dry finish, and short playtime on skin — sensory characteristics that traditionally&nbsp;required&nbsp;volatile silicones.&nbsp;Formulation analysis comparing&nbsp;hemisqualane&nbsp;and D5 replacements&nbsp;notes that it excels in delivering initial slip and lightness, making it well suited to facial serums, primers, and light-texture body products.&nbsp;



Its limitation is that it does not fully replicate silicone volatility: unlike D5,&nbsp;hemisqualane&nbsp;does not evaporate from the skin surface, so in formulations that rely on evaporation for texture change or pigment setting, performance adjustments may be required.&nbsp;ScienceDirect research on bio-based D5 alternatives&nbsp;recommends blending&nbsp;hemisqualane&nbsp;with other light bio-alkanes or esters to reconstruct a complete volatile profile.&nbsp;



Formulation Positioning&nbsp;







Summary



Squalane and&nbsp;hemisqualane&nbsp;occupy distinct but complementary positions in sustainable formulation. Squalane addresses the&nbsp;emolliency&nbsp;and barrier-support function with a body of&nbsp;dermatological evidence spanning TEWL reduction, collagen protection, and active delivery enhancement.&nbsp;Hemisqualane&nbsp;targets the regulatory gap left by the restriction of cyclic silicones, offering a biodegradable, bio-based alternative with a sensory profile close enough to D5 to allow meaningful reformulation.&nbsp;



Both&nbsp;benefit&nbsp;from the same fermentation platform that has resolved the supply, consistency, and sourcing challenges that historically limited plant-derived squalane. For formulators&nbsp;operating&nbsp;under the EU REACH framework — or&nbsp;anticipating&nbsp;equivalent restrictions in other markets — the case for integrating these molecules into the emollient toolkit is now as much regulatory as it is scientific.&nbsp;


Squalane and Hemisqualane: Sustainable best-in-class Emollient Alternatives 


A cosmetic product that cannot resist microbial contamination will fail the consumer before the active ingredients ever have a chance to work. Preservation is not a regulatory formality — it is a fundamental safety function. And because bacteria, yeast, and mould exploit different biochemical niches, achieving genuine broad-spectrum efficacy requires understanding what each class of organism needs, how different preservative chemistries interrupt those needs, and why single-agent systems are almost never sufficient. 



Why Formulations Are Vulnerable 



Any product&nbsp;containing&nbsp;water provides a medium in which microorganisms can grow, given the right conditions of temperature, pH, and nutrient availability.&nbsp;The PMC review&nbsp;on cosmetics preservation strategies&nbsp;notes&nbsp;that&nbsp;virtually all&nbsp;cosmetic ingredients are biodegradable to some degree — emollients, thickeners, humectants, and surfactants all provide sufficient nutrient substrate to support microbial proliferation.&nbsp;



Contamination routes are multiple: raw materials, process water, manufacturing equipment, packaging, and consumer use.&nbsp;Research on microbial contamination in cosmetics&nbsp;identifies&nbsp;bacteria (Staphylococcus epidermidis,&nbsp;Bacillus cereus,&nbsp;Bacillus&nbsp;circulans) and&nbsp;moulds&nbsp;(Aspergillus versicolor) as organisms recovered from real-world contaminated products, including in&nbsp;personalised&nbsp;cosmetic systems.&nbsp;



The regulatory framework reflects this risk. EU Regulation 1223/2009 lists&nbsp;permitted&nbsp;preservatives in Annex V, with concentration limits and conditions of use regularly reviewed by the SCCS (Scientific Committee on Consumer Safety). Formulators are not free to use any antimicrobial agent: only listed substances, within listed limits, for listed product categories. Regulatory compliance therefore&nbsp;sets&nbsp;the outer boundary of the design space before any formulation decision is made.&nbsp;



The Three Targets: Bacteria, Yeast, and Mould 



Bacteria 



Bacteria are the fastest-replicating contaminants under typical cosmetic storage conditions. The challenge panel defined by&nbsp;ISO 11930:2019&nbsp;— the primary international standard for&nbsp;preservation&nbsp;efficacy testing — includes three bacterial species:&nbsp;Staphylococcus aureus&nbsp;(Gram-positive),&nbsp;Escherichia&nbsp;coli&nbsp;and&nbsp;Pseudomonas aeruginosa&nbsp;(Gram-negative). The inclusion of both Gram-positive and Gram-negative strains is deliberate: their cell wall architecture differs&nbsp;fundamentally, and many preservatives act effectively on one class while being poorly active against the other.&nbsp;



Gram-negative bacteria are&nbsp;generally harder&nbsp;to inhibit because their outer membrane presents an&nbsp;additional&nbsp;lipopolysaccharide barrier that restricts the entry of many amphiphilic molecules.&nbsp;Pseudomonas aeruginosa&nbsp;in particular is&nbsp;frequently&nbsp;described as the most challenging organism in challenge testing, combining this structural resistance with metabolic versatility and the ability to degrade certain preservative molecules.&nbsp;



Yeast 



The most common yeast contaminant in cosmetics is&nbsp;Candida albicans, an opportunistic pathogen capable of causing skin and mucosal infections. Yeasts are eukaryotes — their cellular&nbsp;organisation&nbsp;is closer to mammalian cells than bacteria, which constrains the preservative chemistries that can target them selectively without skin cell toxicity concerns.&nbsp;



PMC research&nbsp;on&nbsp;ethylhexylglycerin&nbsp;and phenoxyethanol&nbsp;synergy&nbsp;demonstrates&nbsp;that yeasts, like Gram-positive bacteria, are susceptible to agents that disrupt plasma membrane integrity — consistent with their lack of an outer membrane equivalent.&nbsp;



Mould 



Mould contamination, primarily from Aspergillus brasiliensis (formerly A. niger) in the ISO 11930 panel, poses a specific challenge: moulds grow more slowly than bacteria but are highly resistant to many preservative systems and can survive as dormant spores. PMC research on sorbic acid against Aspergillus niger confirms that conidia (spores) can require three times the minimum inhibitory concentration required for established mycelium — meaning preservative systems that control active growth may fail to prevent germination from contaminating spores. 



Preservative Families and Their Mechanisms 



Organic Acids 



Organic acids — including benzoic acid, sorbic acid, and&nbsp;their salts&nbsp;— are among the oldest and best-characterised&nbsp;preservatives. Their antimicrobial mechanism is&nbsp;pH-dependent&nbsp;and exploits membrane permeability: at low pH, the undissociated, lipophilic acid form penetrates the plasma membrane freely. Once inside the cell, where pH is&nbsp;maintained&nbsp;near neutral, the acid dissociates, releasing protons and generating intracellular acidification.&nbsp;



PMC research&nbsp;on&nbsp;MIC values of sorbic and benzoic acids across 57 microorganism strains&nbsp;confirms&nbsp;the strong pH dependence: efficacy is&nbsp;substantially higher&nbsp;at pH 4.5 than at pH 6.0. This creates a direct formulation constraint — organic acids lose preservative function rapidly as&nbsp;product pH rises above 5.5–6.0, making them unsuitable as sole preservatives in neutral or near-alkaline systems (moisturisers, conditioners, many rinse-off products).&nbsp;



Sorbic acid and potassium sorbate are primarily effective against yeast and&nbsp;mould; benzoic acid extends coverage to bacteria.&nbsp;PubMed data&nbsp;on sorbic acid inhibitory concentrations against&nbsp;B. subtilis,&nbsp;E. coli,&nbsp;P. aeruginosa,&nbsp;S. aureus, and&nbsp;C. albicans&nbsp;shows that the undissociated acid is 10 to 600 times more active than its dissociated form — underscoring why pH management is inseparable from acid-based preservation design.&nbsp;



Phenols and Phenoxyethanol 



Phenoxyethanol is among the most surveyed preservatives in market products. A&nbsp;study&nbsp;of 325 commercial cosmetics found phenoxyethanol appearing across leave-on and rinse-off formats, at concentrations permitted up to 1% under EU and Chinese regulations.&nbsp;



Its mechanism, detailed in&nbsp;a ScienceDirect review&nbsp;on preservative action,&nbsp;operates&nbsp;through membrane disruption: phenoxyethanol&nbsp;permeabilises&nbsp;and&nbsp;solubilises&nbsp;the cell envelope and plasma membrane of both Gram-positive and Gram-negative bacteria, and induces rapid leakage of potassium ions from&nbsp;E. coli,&nbsp;P. aeruginosa,&nbsp;S. aureus, and&nbsp;Enterococcus faecium. Its activity against fungi is real but weaker, which is why it is&nbsp;almost universally&nbsp;combined with a fungicidal co-preservative in practice.&nbsp;



Parabens (methyl-, ethyl-, propyl-, butylparaben) share the phenolic pharmacophore and have been the dominant preservative family in cosmetics for decades. Their broad-spectrum coverage — bacteria, yeast, and&nbsp;mould&nbsp;— at concentrations typically below 0.4% made them the default choice for complex emulsion systems. Their current regulatory status is stable for short-chain grades (methyl and ethyl), which the SCCS has confirmed as safe; long-chain grades face restrictions on endocrine disruption concerns.&nbsp;



Ethylhexylglycerin as Booster 



Ethylhexylglycerin (EHG) is classified as a preservation booster rather than a standalone preservative. Research on EHG and phenoxyethanol interactions establishes its mechanism: EHG reduces surface tension at the microbial cell membrane, increasing permeability and thereby allowing co-preservatives to penetrate more effectively. It enhances the activity of phenoxyethanol, dehydroacetic acid, benzyl alcohol, and methylparaben, enabling lower total preservative loads while maintaining efficacy. Its additional moisturising and skin-conditioning properties make it a common choice in formulations targeting "clean beauty" positioning. 



Chelating Agents 



Ethylenediaminetetraacetic acid (EDTA) functions as a preservative potentiator rather than an active antimicrobial. By chelating divalent metal ions (Ca²⁺, Mg²⁺) from the outer membrane of Gram-negative bacteria, EDTA destabilises the lipopolysaccharide layer, making cells permeable to agents that would otherwise be excluded. Its primary value is therefore in extending the activity of existing preservatives against P. aeruginosa and other intrinsically resistant Gram-negative species. 



Validating the System: ISO 11930 and the Challenge Test 



A preservative system is not&nbsp;validated&nbsp;by ingredient selection alone.&nbsp;ISO 11930:2019&nbsp;—&nbsp;Cosmetics — Microbiology — Evaluation of the antimicrobial protection of a cosmetic product&nbsp;— defines the standard framework for preservation efficacy testing (PET), also called the challenge test.&nbsp;



The protocol involves inoculating five separate product samples with calibrated suspensions of&nbsp;S. aureus,&nbsp;E. coli,&nbsp;P. aeruginosa,&nbsp;C. albicans, and&nbsp;A.&nbsp;brasiliensis&nbsp;(each at ≥10⁵ CFU/g or mL), then measuring&nbsp;viable&nbsp;counts at defined intervals over 28 days. Two acceptance criteria are defined: Criteria A (stricter, typically&nbsp;required&nbsp;for leave-on products with elevated consumer risk) and Criteria B (less strict, applicable to lower-risk formats such as rinse-off products). Both&nbsp;require&nbsp;defined log reductions within specified&nbsp;timeframes&nbsp;— not just&nbsp;absence&nbsp;of visible growth.&nbsp;



The test applies to water-containing products or those where water forms the internal phase. Products qualifying as microbiologically&nbsp;low risk&nbsp;under ISO 29621 risk assessment criteria may be exempt.&nbsp;



Formulation Variables That Affect Preservation 



Preservation efficacy is never solely a function of the preservative itself — it is a&nbsp;system&nbsp;property. Several formulation variables interact:&nbsp;




pH&nbsp;is the single most influential variable for acid-based&nbsp;systems, and&nbsp;has secondary effects on most other preservatives through its influence on membrane charge and&nbsp;ionisation. Formulators should verify preservative efficacy at the actual final pH, not at a nominal target.&nbsp;



Water activity (aw)&nbsp;determines&nbsp;availability&nbsp;of free water for microbial growth. Products with high glycerol or sorbitol content effectively reduce water activity and can reduce the preservative burden&nbsp;required&nbsp;— a rationale for reduced-preservative formulations based on multifunctional humectants.&nbsp;



Emulsion type and phase partitioning.&nbsp;Most preservatives are more active in the aqueous phase. In a high-internal-phase W/O emulsion, the ratio of&nbsp;preservative&nbsp;distributed to the aqueous phase versus the oil phase matters for efficacy.&nbsp;The rheology modifier&nbsp;article on leave-on versus rinse-off formulations addresses the formulation architecture differences across product types — a relevant context when specifying preservation, since the same preservative system may behave differently across those formats.&nbsp;



Packaging&nbsp;affects microbial exposure: airless dispensers and tubes that prevent re-introduction of ambient microorganisms on repeated use reduce the contamination challenge&nbsp;relative&nbsp;to wide-mouth jars. ISO 29621&nbsp;formalises&nbsp;this risk assessment.&nbsp;



Ingredient interactions.&nbsp;Anionic polymers (carbomers, xanthan gum) can bind cationic preservatives and reduce their free active concentration. Non-ionic surfactants can&nbsp;solubilise&nbsp;preservatives into micelles, reducing their aqueous activity. These interactions must be accounted for in formulation design, not&nbsp;assumed away.&nbsp;




Preservation in Natural and "Clean" Formulations 



Consumer and regulatory pressure on conventional preservatives&nbsp;has&nbsp;driven significant reformulation activity, particularly around parabens,&nbsp;isothiazolinones, and formaldehyde releasers.&nbsp;PMC research&nbsp;on natural antimicrobial compounds&nbsp;identifies&nbsp;plant phenolics, peptides, and essential oil constituents as candidates for natural preservation systems — but notes that broad-spectrum activity at cosmetically acceptable concentrations&nbsp;remains&nbsp;the central challenge.&nbsp;



Phenolic compounds from plant sources (thymol, carvacrol, eugenol) show genuine antibacterial activity, but their&nbsp;odour&nbsp;profile, skin&nbsp;sensitisation&nbsp;potential, and formulation compatibility limit their practical use. Combinations of multiple natural agents with complementary mechanisms — mirroring the multi-preservative approach used with synthetic systems — are&nbsp;emerging&nbsp;as the more&nbsp;viable&nbsp;strategy.&nbsp;



The fundamental constraint does not change: any preservation system, whether conventional or natural, must pass the ISO 11930 challenge test before a product reaches market. Challenge test data is&nbsp;required&nbsp;in the Cosmetic Product Safety Report (CPSR) under EU Regulation 1223/2009, and a natural label does not exempt a product from this requirement.&nbsp;



For an overview of how preservation fits within the broader personal care ingredient portfolio — including the multifunctional ingredients that can reduce preservative dependency covers preservation systems alongside surfactants and rheology modifiers in a regulatory-compliant framework.&nbsp;



Summary: Designing for the Spectrum 



Achieving reliable broad-spectrum preservation means designing across three independent microbiological targets simultaneously:&nbsp;




Bacteria require agents active against both Gram-positive and Gram-negative cell architectures — meaning at minimum a membrane-disrupting agent (phenoxyethanol, parabens) combined with a chelator (EDTA) to address Gram-negative outer membrane resistance. 





Yeast requires agents with fungistatic activity — typically shared by parabens and phenoxyethanol at standard use concentrations, but often requiring confirmation in challenge testing given yeast resistance variation. 





Mould demands attention to spore germination, not just mycelial growth — meaning that efficacy at ≤MIC for established mycelium is insufficient as a specification target. 




The formulator's toolkit for broad-spectrum preservation is well&nbsp;characterised: the mechanisms are understood, the validation pathway is&nbsp;standardised, and the regulatory framework is clear. What requires judgement is the system design — matching preservative chemistry to&nbsp;formulation&nbsp;pH, product format, emulsion type, and ingredient interactions, then verifying the result empirically before the product reaches the consumer.&nbsp;


Broad-Spectrum Preservation — Bacteria, Yeast and Mould 


Any plastic part entering the European Union in 2026 has to clear two hurdles at once: does it meet the fire safety requirements for its application, and is the flame retardant chemistry it uses still legally permitted? For engineering plastics in electrical and electronic equipment, automotive components, construction, and appliances, these two questions are harder to align than they were a few years ago. Regulatory pressure on halogenated compounds — brominated flame retardants especially — has been building since the RoHS restrictions of 2006, and 2026 brings specific milestones worth tracking.



This article covers the current state of EU flame retardant compliance: what is restricted, what is under active review, and what halogen-free alternatives actually deliver — so compounders and procurement teams can make formulation decisions ahead of regulatory deadlines.



For a broader overview of REACH 2026 — SVHC candidate list updates, PFAS restriction progress, and more — see Safic-Alcan’s REACH 2026 restricted substances article.





What Flame Retardants Do in Plastics — and Why the Chemistry Matters



Flame retardants are synthetic chemicals that prevent materials from igniting and slow fire spread. They enter plastic products either as additives blended during compounding or as reactive compounds built into the polymer backbone during polymerization. In plastic materials, the additive approach is more common: the flame retardant is mixed into the polymer resin during compounding, changing how the finished part burns without altering the polymer chain itself.



Flammability in plastics is not a fixed property — it depends on the polymer, the additive package, part geometry, and the fire scenario. Flame retardants can give flammable polymers flame retardant properties and reduce fire risk. UL 94 classifications — from HB (horizontal burn) to V-0 (self-extinguishing within 10 seconds) — define the performance thresholds different applications require. A domestic appliance housing must meet a different standard than a printed circuit board substrate, and each target classification drives a different flame retardant loading and chemistry.



Flame retardant selection is both a performance and a regulatory decision. The chemistry options are broad — flame retardants comprise halogenated (including brominated), organophosphorus, nitrogen-based, intumescent systems, and various organic/inorganic compounds — but regulatory constraints on which substances are permitted in which applications narrow that space considerably.



Brominated Flame Retardants: The Regulatory Story



PBDEs and the RoHS directive



Brominated flame retardant restriction in the EU did not start with REACH — it started with RoHS. The RoHS directive requires the restriction of these hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE), in electrical and electronic equipment. Since 2006, PBBs and PBDEs have been prohibited above 1,000 ppm in any homogeneous material in electrical and electronic products — so a plastic housing, resin substrate, or cable sheath containing a restricted brominated compound above that threshold fails RoHS, regardless of fire performance.



Polybrominated diphenylethers (PBDEs) are now banned or restricted in many countries because of their persistence, bioaccumulation potential, and toxicity. High lipophilicity — log Kow values between 5.74 and 8.27 — drives their persistence, bioaccumulation, and biomagnification in the environment. Half-lives of certain congeners in the human body range from one to twelve years. Penta- and octa-BDE commercial mixtures have been listed as persistent organic pollutants (POPs) under the Stockholm Convention.



REACH and the expanding SVHC landscape



REACH operates through a different mechanism — it applies to all articles placed on the EU market, not just electrical and electronic equipment. Several brominated flame retardant compounds are already on the SVHC (Substances of Very High Concern) Candidate List, which means articles containing them above 0.1% by weight must be disclosed to downstream customers and, in B2C supply chains, to consumers on request.



In January 2026, ECHA opened a formal Call for Evidence on certain non-polymeric aromatic brominated flame retardants in electrical and electronic products, construction products, and textiles — running from January 21 to March 18, 2026. A restriction proposal under Annex XVII of REACH is in preparation. Affected sectors — electronics, construction plastics, textile compounds — should expect a regulatory deadline in months rather than years.



RoHS and REACH are not the same compliance standard. RoHS compliance does not mean halogen-free. PBBs and PBDEs are just two entries in the broader category of brominated flame retardants. Many other brominated substances remain in use — but are candidates for future SVHC listing or Annex XVII restriction. Formulators who have cleared RoHS but not reviewed their full BFR inventory against the REACH candidate list have an open compliance gap.



Alternative BFRs: not automatically safer



When PBDEs were restricted, the market moved to alternatives — compounds such as decabromodiphenyl ethane (DBDPE) and tribromophenol — that offered comparable fire performance without the structures named in existing restrictions. The problem is that there is a wide range of alternative BFRs that may possess similar hazardous properties to the compounds they replaced, and for many of them PBT (persistence, bioaccumulation, toxicity) data is thin. ECHA’s restriction work on non-polymeric aromatic brominated flame retardants addresses that directly: substance-by-substance restriction tends to produce substitution cycles rather than a genuine shift to safer chemistry.



Halogen-Free Flame Retardants: Performance Grades for Plastics



Most compounders have been developing halogen-free flame retardant (HFFR) alternatives for over a decade — the regulatory direction has been clear for long enough. The transition is more advanced in electrical and electronic equipment than in construction plastics and automotive components, where the mechanical and thermal performance requirements are more demanding. What each HFFR chemistry class actually delivers — and where it falls short — matters for any formulation decision.



Phosphorus-based flame retardants



Phosphorus-based compounds are the main halogen-free alternative across most engineering plastic matrices. Phosphorus-containing flame retardants can be utilized as additives or incorporated into the polymer chain during polymerization, and act in the condensed or gaseous phase depending on their chemistry and the host polymer. In the condensed phase, thermal decomposition produces phosphoric acid structures that promote char formation — a protective layer that limits heat and mass transfer during combustion. This mechanism works particularly well in oxygen-containing matrices such as polyesters, polyamides, and ester-linked resins.



Reactive flame retardants have the advantages of little influence on the physical properties of polymers and low tendency to migrate out . Driven by demand for non-halogenated options, phosphorus-based compounds have become the main alternative in polyurethane, PPS, polyamide, and other engineering polymer systems. The main limitation is cost: the cost of halogen-free flame retardant plastics is higher than that of halogenated plastics, which is why achieving V-0 classification at the lowest viable additive loading remains an active focus of formulation work.



Aluminum diethylphosphinate and ammonium polyphosphate are the most widely used phosphorus-based additive systems in engineering plastics. In ABS and PC/ABS alloys — common in appliance housings and consumer electronics — phosphorus-based flame retardant additives provide a more environmentally friendly alternative to halogenated systems, though their effect on impact energy requires optimization of loading levels and particle morphology.



Synergistic systems and intumescent formulations



Single-chemistry flame retardant systems rarely hit all targets at once — fire performance, mechanical durability, and processing compatibility tend to pull in different directions. Most current HFFR formulations use synergistic mixtures: a primary flame retardant combined with a synergist that amplifies its effectiveness, reducing the total additive loading needed and preserving more of the base polymer’s properties.



Phosphorus-nitrogen synergistic systems work well in polyolefin matrices such as polypropylene, where phosphorus alone has limited condensed-phase activity. The nitrogen component drives intumescence — the char layer physically swells during combustion, forming an insulating barrier that slows heat transfer to the unburned polymer below. Flame retardants are incorporated into textiles, construction materials, electronics, and consumer products through physical addition — and this intumescent approach is now standard in construction plastic applications such as cable management systems, pipe insulation, and structural panels, where UL 94 V-0 or European Euroclasse B and C fire classifications apply.



Research into nanocomposite approaches — layered double hydroxides or organoclays combined with phosphorus flame retardants — shows performance gains in demanding polymer systems, though cost keeps them out of commodity plastic formulation for now.



Inorganic flame retardants: aluminum trihydrate and magnesium hydroxide



In cost-sensitive applications where processing temperatures allow — principally polyolefins, PVC compounds, and cable insulation — aluminum trihydrate (ATH) and magnesium hydroxide (MDH) deliver flame retardancy without hazardous substance concerns. Both release water vapor during decomposition, diluting combustible gases and cooling the combustion zone. High loadings are required (40–65% by weight), which limits their use where mechanical properties need to be preserved.



From a regulatory standpoint, both are clean: no SVHC status, no REACH or RoHS restrictions, and compatible with recyclability requirements. Wire and cable insulation for infrastructure applications is their natural home, where the Construction Products Regulation and the Low Voltage Directive impose fire safety and environmental requirements at the same time.



Practical Compliance in 2026: What Formulators Need to Do




Audit the full BFR inventory. RoHS addresses PBBs and PBDEs — REACH’s SVHC list goes further. The restriction proposal on non-polymeric aromatic brominated flame retardants (Call for Evidence, January 2026) covers substances used in electrical and electronic products, construction products, and textiles. Any compounder using brominated flame retardants in these applications should check each compound’s SVHC status and watch the ECHA restriction timeline.



Understand the RoHS–REACH interaction. Passing one does not mean passing the other. Articles containing SVHC Candidate List substances above 0.1% by weight require disclosure to the downstream supply chain — whether or not those substances appear in RoHS. Electronics manufacturers sourcing plastic compounds need to verify SVHC presence, not just RoHS compliance.



Evaluate phosphorus-based alternatives against the full performance specification. Halogen-free phosphorus systems can match brominated flame retardants on UL 94 classification in many engineering polymer matrices, but their effect on tensile strength, elongation, thermal stability, and processing needs to be validated at the compound level. The interaction with the base resin — especially in PPS, polyamide, and ABS/PC blends — cannot be predicted from chemistry alone.



Plan for PFAS exposure in fluoropolymer-based formulations. PFAS restrictions are moving through a separate regulatory track, but formulators using fluoropolymers as processing aids or in specialty flame retardant systems should note that ECHA’s SEAC opinion on the broad PFAS restriction is expected by end of 2026, with a Commission decision likely afterward. Any compound system relying on fluoropolymer components needs to be assessed for regulatory exposure alongside BFR compliance.





Flame Retardants in Plastics — EU REACH Compliance 2026


A formulator choosing between two dimethicone grades&nbsp;isn't&nbsp;making a marginal adjustment —&nbsp;they're&nbsp;choosing between a fast-spreading, dry-touch emollient and a high-viscosity silicone fluid with&nbsp;very different&nbsp;slip, barrier, and sensorial profiles. The most common silicone compounds in personal care — dimethicone,&nbsp;cyclopentasiloxane, phenyl&nbsp;trimethicone&nbsp;— each span multiple grades, and each grade delivers a distinct set of behaviors in a finished cream, serum, or hair product. The viscosity number printed on a silicone specification sheet encodes functional behaviors that&nbsp;determine&nbsp;how a product feels at pick-up, how it spreads across skin, whether it leaves a long-lasting film or evaporates cleanly, and how it behaves over a day of wear. Getting that number wrong means rebuilding the formulation.&nbsp;&nbsp;



This article maps the major silicone grades used in personal care — volatile&nbsp;cyclics, linear&nbsp;dimethicones&nbsp;across the viscosity spectrum, phenyl-functional fluids, amino-functional silicones, and crosslinked elastomers — and explains what each grade&nbsp;actually delivers&nbsp;in a finished product. To explore&nbsp;Safic-Alcan's&nbsp;silicone ingredients for personal care, the catalogue provides a searchable starting point by application and grade. For a broader view of the cosmetics ingredient portfolio, the&nbsp;personal care product range&nbsp;covers emollients, film-formers, and functional additives across all categories.&nbsp;&nbsp;





Why Silicone Grade Matters More Than Silicone Type&nbsp;&nbsp;



Silicones are synthetic polymers built on a silicon-oxygen backbone with organic side groups. By changing molecular weight, crosslink density, or surface functionality, manufacturers create materials that behave as fast-evaporating carriers, viscous emollients, cushiony elastomers, or surface-active modifiers. This flexibility is why silicones appear across skin care, color cosmetics, hair care, and sun care, and why grade selection is the consequential decision.  



The performance characteristics of silicones are&nbsp;derived from molecular attributes&nbsp;including backbone flexibility, low intermolecular interactions, large distances between molecules, the nature of organic side groups, and the stability of bonds between atoms. The repeating siloxane unit — two methyl groups attached to a silicon atom bridged by oxygen — gives silicones their characteristically low surface tension, which explains their exceptional&nbsp;spreadability&nbsp;on skin. Those molecular differences&nbsp;show up&nbsp;directly in the behaviors that matter to formulators:&nbsp;spreadability, skin feel, volatility, film persistence, and compatibility with other ingredients.&nbsp;&nbsp;



Silicone-based ingredients are also chemically inert: they do not react with&nbsp;the vast majority of&nbsp;cosmetic actives, preservatives, or emulsifiers, which is why&nbsp;they're&nbsp;used as carrier fluids and texture agents without triggering irritation or destabilizing formulations. Silica — the ultimate degradation product of silicones — is a naturally occurring mineral, which supports their favorable environmental and toxicological profile. For context: silicones have been used in personal care since the 1950s and are&nbsp;among the most extensively safety-tested&nbsp;class of cosmetic ingredients available.&nbsp;&nbsp;



Volatile Silicones: The Carrier Grade&nbsp;&nbsp;



Cyclopentasiloxane&nbsp;(D5) and its functional role&nbsp;&nbsp;



Cyclopentasiloxane&nbsp;(D5) is a lightweight, odorless, water-thin silicone whose defining property is volatility. It evaporates from skin after application, leaving behind active ingredients, film-formers, or conditioning agents without any greasy or occlusive residue.&nbsp;Roughly 90% of it disappears&nbsp;into the air within hours of application. That volatility is the intended mechanism of action.&nbsp;&nbsp;



D5 is a delivery vehicle: it carries heavier, more functional ingredients — silicone elastomers, conditioning actives, UV filters — onto skin or hair, then steps aside. Antiperspirants use D5 to coat the skin without post-application tackiness. Foundations and primers use it to achieve a smooth, non-greasy&nbsp;initial&nbsp;feel while the active pigment or film-former&nbsp;remains&nbsp;evenly distributed. Hair serums use it to carry conditioning silicones along the hair shaft before evaporation&nbsp;concentrates&nbsp;the deposited film. In cream and lotion emulsions, D5 is&nbsp;frequently&nbsp;incorporated as a silicone fluid phase&nbsp;component&nbsp;to reduce the heavy feel associated with high oil-phase content, and in silicone emulsions it acts as the continuous non-aqueous phase that carries functional compounds to the skin surface.&nbsp;&nbsp;



Regulatory position of D5&nbsp;&nbsp;



The EU, under REACH, restricts D5 in rinse-off cosmetics (shampoos, body washes) at concentrations above 0.1%, based on concerns about aquatic accumulation via wastewater. Leave-on products face fewer current restrictions because the ingredient evaporates into the atmosphere rather than washing into waterways, and studies show that significant amounts of  D5 in leave-on products evaporate during typical use, leaving a negligible fraction available to enter wastewater. However, formulators should monitor the regulatory trajectory: the clean beauty market is applying additional pressure on cyclic silicones independent of formal regulatory status.  



Linear&nbsp;Dimethicones: The Viscosity Spectrum&nbsp;&nbsp;



Dimethicone&nbsp;(polydimethylsiloxane, PDMS) is the&nbsp;workhorse&nbsp;silicone fluid in personal care formulation. As a compound, it is a linear polymer of repeating&nbsp;dimethylsiloxane&nbsp;units, and its viscosity — expressed in centistokes (cSt) — runs from under 5&nbsp;cSt&nbsp;to over 100,000&nbsp;cSt. Each range of that spectrum delivers meaningfully different performance in a finished cosmetic.&nbsp;&nbsp;



Low viscosity grades (5–50&nbsp;cSt): lightweight emollience&nbsp;&nbsp;



At the low end of the viscosity range, dimethicone grades behave almost like volatile carriers, spreading rapidly across skin and leaving a very light, non-greasy feel. Ultra-low viscosity grades (below 5 cSt) are engineered to evaporate faster than alcohol and have niche applications in foaming formats and aerated textures. Grades in the 5–20 cSt range provide a soft, velvety feel when applied to hair and skin, with a hydrophobic, breathable barrier character that does not occlude the skin surface. These grades are well-suited to light lotions, body fluids, and spray formats where after-feel must be minimal.  



Mid-viscosity grades (100–350&nbsp;cSt): the formulation standard&nbsp;&nbsp;



The 200–350 cSt range is the most commonly used dimethicone viscosity range in skin care. Dimethicone 350 cSt adds slip and reduces tackiness while delivering conditioning and barrier properties across both skin and hair applications. It improves the feel of cream and lotion products, contributes spreadability without heaviness, and is compatible with most emulsion formats as an oil-phase component. Its functional balance — enough body to contribute texture, light enough to avoid greasiness — makes it the reference grade for general-purpose skin care and the starting point for most formulation screening. In silicone-based emulsions, it is often used alongside an emulsifier to create stable water-in-silicone or oil-in-water systems with a distinctive silky after-feel.  



Mid-viscosity&nbsp;dimethicones&nbsp;also contribute&nbsp;low friction coefficients&nbsp;measured around 0.02–0.05, versus over 0.3 for many traditional oils. This difference is what gives silicone-based skin care products their characteristic slip and ease of application, and is directly relevant to foundation&nbsp;spreadability, pigment dispersion in color cosmetics, and sunscreen application uniformity across the skin surface.



High viscosity grades (1,000&nbsp;cSt&nbsp;and above): conditioning film and hair care&nbsp;&nbsp;



At 1,000&nbsp;cSt&nbsp;and above,&nbsp;dimethicones&nbsp;become viscous, oil-like fluids that form substantive films on skin and hair. In hair care,&nbsp;dimethicone has the effect of protecting the hair shaft&nbsp;from abrasive actions, while polysiloxane polymers can re-cement lifted cuticle scales and provide protection from heat styling. These high-viscosity grades deposit more persistently than their lighter counterparts — which is an asset in conditioning rinse-off products where deposition efficiency matters, and a potential liability in skin care formulations where a greasy after-feel would be unacceptable.&nbsp;&nbsp;



In leave-on hair products — serums, oils, heat protectants — high-viscosity dimethicone grades provide the film weight necessary for visible gloss, frizz suppression, and cuticle smoothing without requiri



Amino-Functional Silicones: Targeted Deposition on Damaged Hair&nbsp;&nbsp;



Amino silicones introduce amine groups into the polydimethylsiloxane backbone, which gives them a cationic character that drives selective deposition onto damaged or chemically treated hair. The amine functionality significantly improves conditioning performance on hair compared with standard grafted siloxanes, and by matching the interfacial tension of the silicone to the hair surface energy, terminal amino silicones provide increased deposition particularly onto colored and damaged hair.  



Published research quantifying this effect found that amino silicone softeners adsorbed more effectively on hair at lower concentrations than polydimethylsiloxane, and that combing force was reduced to a greater extent by amino silicone treatment — a direct measure of conditioning performance. Adsorption is also enhanced at higher temperatures, which matters for heat-activated treatments and rinse-off conditioners used with warm water.  



The trade-off is selectivity of deposition: amino silicones accumulate on damaged hair zones more efficiently than on healthy&nbsp;cuticle, which can lead to uneven build-up with repeated use in the absence of clarifying steps. This makes them best suited to targeted treatment formats — intensive conditioners, leave-in repair products — rather than everyday cleansing formulations.&nbsp;&nbsp;



Phenyl&nbsp;Trimethicone: The Optical Performance Grade&nbsp;&nbsp;



Phenyl trimethicone is a modified silicone fluid in which phenyl groups replace some of the methyl groups along the siloxane backbone. This substitution has two principal effects on performance: it raises the refractive index to approximately 1.498 (versus around 1.404 for standard dimethicone), which translates to superior light reflection and a glossier finish on both skin and hair; and it improves compatibility with organic oils and natural ingredients that would otherwise have limited miscibility with standard silicones.  



In hair care, phenyl trimethicone's high refractive index makes it the preferred grade when the formulation objective is visible shine rather than just conditioning. Its film forms a water-resistant layer along the hair shaft, providing humidity resistance and frizz control that persists into the day. In color cosmetics and foundation formulations, its optical properties contribute to the luminous, skin-like finish that distinguishes high-end face products. In sunscreen formulations, its enhanced UV stability compared to standard dimethicone helps maintain SPF performance over time.  



Unlike volatile silicones, phenyl&nbsp;trimethicone&nbsp;is non-volatile — it&nbsp;remains&nbsp;on skin or hair as a persistent film. This makes it a leave-on grade by design, inappropriate for rinse-off applications where carry-off efficiency and residue are performance criteria.&nbsp;&nbsp;



Silicone Elastomers (Crosspolymers): The Sensorial Grade&nbsp;&nbsp;



Silicone elastomers — supplied as dimethicone crosspolymer gels or powders — represent a structurally distinct class from the linear silicone fluids. They are crosslinked networks with limited molecular mobility, which gives them a cushiony, bouncy texture entirely unlike any fluid silicone. Silicone elastomer gels provide a dry, non-greasy, silky-smooth skin feel while absorbing quickly onto the skin — a combination of tactile properties that linear silicones alone cannot replicate.  



In practice, elastomers are added to skin care creams, sunscreen formulations, and color cosmetics at 1–10% to modulate texture and sensorial profile. Their crosslinked network structure enables sebum absorption, which reduces shine and&nbsp;maintains&nbsp;a long-lasting matte finish over time — a key performance criterion in primers and long-wear foundations. Their film-forming character also improves&nbsp;spreadability&nbsp;and wear longevity of pigmented formulations, helping pigment stay evenly distributed on skin without creasing or separating. They can also act as stabilizing agents compatible with a variety of lipophilic actives, including UV filters and fragrance compounds.&nbsp;&nbsp;



Elastomers are also used as thickening agents in anhydrous and water-in-silicone emulsions, where their unique rheological behavior — gel-like at rest, yielding smoothly on application — enables formats that would be difficult to achieve with conventional polymer thickeners.&nbsp;&nbsp;



Selecting the Right Grade: A Functional Summary&nbsp;&nbsp;



The grade selection decision comes down to functional&nbsp;objectives:&nbsp;&nbsp;




Delivery and dry-feel priority&nbsp;→ Volatile grade (D5): ideal when the silicone must leave the skin quickly and cleanly, carrying&nbsp;actives&nbsp;or conditioning agents to the surface before evaporating. Subject to regulatory monitoring in rinse-off applications under REACH.&nbsp;&nbsp;



Lightweight emollience and slip&nbsp;→ Low-to-mid viscosity dimethicone (5–350&nbsp;cSt): the standard range for skin care emulsions, body products, and light hair applications. The 200–350&nbsp;cSt&nbsp;grades are the most widely used formulation reference.&nbsp;&nbsp;



Protective film and hair conditioning&nbsp;→ High viscosity dimethicone (1,000&nbsp;cSt+): suited to leave-on hair care and barrier-forming skin care where film persistence and substantivity matter.&nbsp;&nbsp;



Targeted repair on damaged or chemically treated hair&nbsp;→ Amino-functional silicone: the grade of choice for intensive conditioning treatments where selective deposition on damaged zones is a performance&nbsp;objective.&nbsp;&nbsp;



Gloss and optical finish&nbsp;→ Phenyl&nbsp;trimethicone: selected specifically for its high refractive index and light-reflection properties in hair shine products, luminous skin care, and UV-stable sun care.&nbsp;&nbsp;



Texture modulation, matte finish, and wear longevity&nbsp;→ Silicone elastomer (crosspolymer): added to create cushiony, non-greasy texture and absorb sebum in primers, foundations, and long-wear skin care.&nbsp;&nbsp;




Working with a Knowledgeable Supplier&nbsp;&nbsp;



Choosing the right silicone grade requires access to the full spectrum — from volatile&nbsp;cyclics&nbsp;to elastomer gels — and technical guidance on how each grade interacts with the rest of the formulation matrix.&nbsp;Safic-Alcan supports personal care formulators across these categories, providing both the portfolio breadth and the technical&nbsp;expertise&nbsp;to match silicone grade to formulation&nbsp;objective.&nbsp;&nbsp;




Silicones in Personal Care: Performance Grades Explained  


Your shampoo needs to pour smoothly from the bottle, lather generously, then rinse off completely in thirty seconds. Your face serum needs to sit still in its dropper, spread evenly across skin, and stay there — hydrating, delivering actives, and feeling elegant — for the next eight hours. Both products depend on a rheology modifier. But the constraints governing that choice diverge sharply the moment you ask whether the formulation is meant to stay on or be washed off.



For a broader overview of how rheology modifiers work mechanically and which families exist across cosmetic formulation types, the complete cosmetics guide covers the full picture. For rheology modifiers across all industries — paints, rubber, food — the general rheology modifiers article provides a wider frame. 





Why the Leave-On / Rinse-Off Distinction Changes Everything



The distinction isn't just a matter of exposure time. It determines which ingredient levels are regulatory compliant, what sensory profile the consumer will perceive on skin or hair, the electrolyte environment the modifier must survive, and how it needs to perform alongside surfactant systems.



The substitution of synthetic polymers with natural and naturally modified additives is only at the beginning in the cosmetic industry: while this shift has already been accomplished in many rinse-off products, leave-on formulations still rely on traditional polymers in most cases. That gap reflects genuine formulation difficulty, not regulatory inertia, and understanding why is the first step toward choosing the right modifier for each application.



In rinse-off products, the modifier must build enough viscosity to give the product body and sensorial pick-up while remaining compatible with high concentrations of surfactants. In leave-on products, the modifier must maintain viscosity over months of storage, deliver a non-tacky, non-stringy skin feel, and — increasingly — meet biodegradable and COSMOS-compliant criteria without compromising on performance.



Rinse-Off Applications: The Surfactant Compatibility Problem



Why standard thickeners fail in surfactant systems



Shampoos, body washes, conditioners, and cleansers share a common constraint: they're built on surfactant systems, typically anionic or amphoteric, and the continuous aqueous phase is strongly ionic. Shampoo products contain a combination of surfactants for cleansing, plus polymers and sodium chloride as rheological modifiers, and are typically produced as a viscous liquid. That ionic load explains why carbomers — the workhorse of leave-on gel formulation — are a poor fit in rinse-off systems: their viscositybuild collapses in the presence of electrolytes, and they interact poorly with the anionic surfactant micelles that carry the thickening load.



NaCl is the traditional viscosity builder for anionic surfactant systems (typically 1–3%), but its effective range is narrow. At higher concentrations, micellar transition can reverse the viscosity gain. Polymer-based alternatives have progressively displaced salt thickening in more sophisticated rinse-off formulations, particularly in sulfate-free systems where salt thickening is even less effective.



HEC and HPMC: workhorses for aqueous rinse-off systems



Hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC) are the cellulose derivatives most widely used in rinse-off personal care formulations. They are nonionic — a critical advantage — which means they thicken aqueous systems without interacting destructively with anionic or cationic surfactant components. HEC (0.5–1.5%) provides reliable viscosity build independent of electrolyte concentration and tolerates the broad pH range and salt loads typical of cleansing formulations. HPMC adds film-forming capacity, relevant in conditioning rinse-off products where some deposition is desired even after washing.



Both work by chain entanglement: long polymer chains physically intertwine in the aqueous phase, building resistance to flow in proportion to concentration. They do not generate a meaningful yield stress, which means they will not prevent long-term sedimentation — a limitation that matters less in rinse-off products, where the absence of suspended particles simplifies stability management.



Guar and hydroxypropyl guar in rinse-off hair care



In hair care, guar gum and its derivatives have found a niche shaped by compatibility with cationic ingredients. Hydroxypropyl guar is noted for its film-forming and lubricating properties that deliver a smooth feel to skin and hair. In rinse-off shampoo and conditioner formulations, its nonionic character makes it compatible with cationic conditioning agents that would precipitate anionic polymers — a real advantage in two-in-one formats. It thickens surfactant systems and contributes sensorial enhancement at the moment of rinsing.



The cationic derivative, guar hydroxypropyltrimonium chloride, deposits efficiently in rinse-off systems, forming a thin conditioning film that helps retain moisture without feeling greasy or heavy. Its ability to bind to the negatively charged surface of hair during washing and stays after rinsing, making it one of the most effective conditioning polymers for shampoo, particularly in sulfate-free systems where conditioning deposition is otherwise harder to achieve.



Formulating for clarity and viscosity build in rinse-off products



Clear gels in body wash and shampoo present a specific challenge: the rheology modifier must build viscosity without introducing haze, and must remain stable across the salt concentrations generated by the preservative system and any added active. Acrylate-based associative polymers (HASE-type) offer better electrolyte tolerance than standard carbomers and interact with surfactant micelles through a combination of polymer network formation and micellar entanglement. They are a practical solution for building viscosity in surfactant systems while maintaining product clarity.



Leave-On Applications: Permanence, Skin Feel, and Stability



The skin feel imperative



In a leave-on product — a face cream, a serum, a sun care formulation, a conditioner — the consumer's tactile experience doesn't end when they wash their hands. Sensorial profile is a primary selection criterion here, on par with viscosity targets and stability requirements.



The modifier choice directly shapes whether a product feels rich or light, tacky or non-tacky, stringy or short-flow. Carbomers produce a short-flow rheology — gels break cleanly on application rather than forming strings — a texture most consumers prefer in leave-on products. That texture is why carbomers remain the dominant thickener in leave-on serums and facial gels despite their well-known electrolyte sensitivity and neutralization requirement.



For leave-on emulsions, the rheology modifier also participates in emulsion stabilization — preventing creaming, coalescence, and phase separation over a product shelf life of 24 to 36 months. Rheology modifiers in emulsion-based formulations control suspension, prevent syneresis, contributing to the texture and feel of the finished product. The modifier must handle all of that while remaining invisible to the consumer — no grittiness, no residue, no interference with active delivery.



Acrylate crosspolymers in leave-on emulsions and sun care



Acrylates/C10-30 alkyl acrylate crosspolymers (the HASE family, hydrophobically modified) bring improved electrolyte tolerance compared to standard carbomers. They are the preferred choice in vitamin C serums, AHA-based formulations at low pH, and mineral sun care products where the ionic load from inorganic UV filters would destabilize a conventional carbomer gel.



In sun care, the modifier's role extends beyond viscosity build: it must suspend mineral UV filter particles (zinc oxide, titanium dioxide) uniformly in the aqueous phase without settling, and must maintain film-forming efficacy on skin application for photostability. Polymeric additives can improve their efficacy, since uniform distribution on skin depends on how the formulation flows.



Natural biopolymers in leave-on: promise and limitation



In rinse-off products, the transition to natural biopolymers is already largely accomplished; in leave-on formulations, the challenge of matching synthetic polymer performance — particularly on skin feel and long-term stability — means traditional synthetic polymers still dominate. The stumbling block isn't regulatory; it's sensorial: natural gums at the use levels needed for comparable viscosity build often introduce a ropy, stringy flow behavior that reads as low quality in leave-on serums and face creams.



Research on polysaccharide combinations — sclerotium gum, xanthan gum, and carrageenan in synergistic blends — has shown that acrylic rheology modifiers can be replaced in oil-in-water emulsions, though fully replicating synthetic texture profiles requires careful optimization. Hydroxypropyl guar, in its non-cationic form, performs well in leave-on skincare gels: it forms a light, breathable film on the surface rather than seeping into pores or leaving an oily residue, and rinses away easily with water. That makes it interesting in hybrid formats — leave-on products designed for skin types that resist heavier film-forming systems.



Biodegradable options and regulatory pressure



REACH microplastic restrictions and COSMOS certification requirements are progressively narrowing the eligible polymer pool in European personal care formulations, with pressure across both leave-on and rinse-off categories. The exposure route — rinse-off versus leave-on — should drive the polymer architecture selection when substituting biodegradable polymers for legacy synthetics. A biodegradable polymer validated for rinse-off performance should not be assumed to perform equivalently in a leave-on application without dedicated stability and sensorial testing.



Key Decision Variables at the Leave-On / Rinse-Off Boundary



A few formulation parameters consistently differentiate the two contexts:




Electrolyte tolerance. Rinse-off formulations typically operate at higher ionic loads (surfactant salts, salt thickeners, preservation systems). This generally rules out standard carbomers and favors nonionic cellulose derivatives or electrolyte-tolerant associative polymers. Leave-on systems vary more widely — from low-electrolyte serums where carbomers perform well to high-electrolyte mineral sunscreens requiring acrylate crosspolymers.



Use levels. Rinse-off products typically run higher polymer concentrations to compensate for dilution during application. Leave-on products can operate at lower concentrations because the modifier is never diluted, which makes performance at low concentrations a more relevant differentiator when evaluating natural biopolymers against synthetics.



Biodegradable compliance. Regulatory and market pressure toward biodegradable and naturally derived polymers applies in both categories, but the performance bar is higher in leave-on formulations. Formulators choosing natural gums for leave-on personal care formulations need to address compatibility with a broader range of actives, greater susceptibility to microbial challenge over long storage, and the sensorial limitations at higher use levels.



Compatibility with surfactant systems. In rinse-off products, compatibility with anionic, cationic, and amphoteric surfactants is required. The best thickener for a leave-on emulsion — a carbomer gel structure — performs poorly in a shampoo. The best thickener for a sulfate-free shampoo — a guar-xanthan blend — may introduce undesirable skin feel in a face serum.




Working with the Right Supplier



Choosing the right rheology modifier for a leave-on or rinse-off application requires access to a portfolio broad enough to cover both application contexts, and technical support that understands the formulation constraints specific to each. Safic-Alcan, as a specialty chemical supplier active in over 90 countries, supports personal care formulators across these categories — from standard cellulose derivatives for rinse-off systems to acrylate crosspolymers and natural biopolymers for leave-on applications.



Get support from our team to discuss your formulation needs, identify the right rheology modification strategy, and access technical documentation for your specific application.


Rheology Modifiers for Leave-On vs. Rinse-Off Applications: A Formulator's Perspective


TL;DR — Rheology modifiers are critical to cosmetic formulation: they control texture, stability, spreadability, and sensory perception. In skincare and personal care, they are used to build viscosity, stabilise emulsions, suspend actives, and deliver the desired skin feel. The right choice depends on pH, electrolyte load, formulation type (gel, emulsion, anhydrous), and target sensory profile.



Why rheology matters in cosmetic formulations



In cosmetics, rheology is not an abstract concept — it directly defines how a product behaves from the moment it leaves the packaging to its final perception on skin.



A cream that is too fluid will separate. A gel that is too rigid will not spread. A serum that feels sticky will be perceived as low quality, regardless of its active ingredients.



Rheology modifiers are therefore used to control:




Texture and viscosity (cream, gel, fluid)



Stability (prevent phase separation and sedimentation)



Spreadability and absorption



Sensory profile (light, rich, cushiony, dry touch)




A rheology modifier is any ingredient added to change how a formulation flows: its viscosity, its yield stress, its thixotropy, and its gel strength. For a broader overview of how these ingredients work across formulation types, our rheology modifiers guide covers the full landscape across cosmetics and coatings.





How rheology modifiers work in cosmetics?



Three core mechanisms are at play in cosmetic formulations.



Chain entanglement is the simplest: long polymer chains dissolve into the aqueous phase and physically intertwine, increasing resistance to flow proportionally to concentration. Hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC) work primarily through this entanglement mechanism. The result is smooth, stable viscosity — but no yield stress, meaning particles will eventually settle.



Associative networking is more sophisticated. Polymers carrying hydrophobic groups form reversible physical bonds between themselves and with the emulsion droplets or pigment particles in the system, building a three-dimensional network that thickens strongly at rest and breaks down under shear.. The network reforms when shear stops, giving genuine thixotropic behaviour — useful for suspending actives, preventing sedimentation, and resisting sag.



Covalent crosslinking creates a permanent network with a defined yield stress. Carbomers — crosslinked polyacrylic acid polymers — are the primary example in cosmetics. They resist flow until a threshold force is exceeded, then yield cleanly. This gives the short, non-stringy skin feel consumers associate with premium gels and serums.



The three families of cosmetic rheology modifiers



Rheology modifier selection table 



Use the table as a first filter. Confirm the final choice with the supplier TDS and a stability test in your own base







1. Natural polymers



Natural-origin polysaccharide thickeners are biocompatible, biodegradable, and highly marketable in clean beauty contexts. The most formulation-relevant are xanthan gum, guar gum, carrageenan, and cellulose derivatives.



Xanthan gum is produced by bacterial fermentation of carbohydrates. It provides strong shear-thinning behaviour, excellent stability across a broad pH range, and good electrolyte tolerance — making it the go-to choice for sulfate-free shampoos, natural gels, and formulations with high salt or ionic load. At concentrations above approximately 0.5%, it delivers a yield value sufficient to suspend particles and prevent settling. Its main limitation is a characteristic ropy skin feel at higher concentrations that requires careful dosage management.



Guar gum is extracted from the endosperm of the guar bean and is nonionic — a significant advantage, since it is compatible with cationic conditioning agents that would precipitate anionic polymers like xanthan or carbomer. The well-documented synergy between guar and xanthan gum — where xanthan's double helix interacts with guar's mannan segment — produces synergistically enhanced viscosity and a combination of shear-thinning flow and meaningful yield stress that neither ingredient achieves alone.



Carrageenan is a sulphated polysaccharide from red seaweed with three sub-types differing in gelling tendency. It has demonstrated efficacy in sunscreen emulsions and structured body care and is a primary candidate in eco-design reformulation programs replacing synthetic acrylics in oil-in-water emulsions.



Cellulose derivatives — HEC and HPMC principally — are semi-synthetic, produced by chemical modification of wood-pulp cellulose. They are non-ionic, compatible with a broad range of actives and electrolytes, and easy to incorporate. They work well as straightforward viscosity builders in surfactant systems and emulsions but lack the suspension performance of anionic systems with a defined yield stress.



The natural challenge. Natural polymers generally require higher use concentrations than synthetic equivalents to achieve comparable performance, and they are more susceptible to microbial growth and batch variability. Research published in Cosmetics (MDPI) has confirmed that acrylic rheological modifiers can be replaced by polysaccharide combinations — sclerotium gum, xanthan gum, diutan gum, and carrageenan — in oil-in-water emulsions, though perfectly replicating synthetic texture profiles requires blending and optimization.



2. Synthetic polymers



Carbomers are crosslinked polyacrylic acid polymers and the dominant synthetic thickener in skin care. They produce exceptionally clear gels, deliver high viscosity at very low usage levels (typically 0.1–0.5%), and create a clean, non-stringy skin feel. They require neutralization with a base to develop viscosity — adding a manufacturing step — and their performance degrades significantly in the presence of salts and electrolytes.



Acrylates/C10-30 alkyl acrylate crosspolymers are hydrophobically modified carbomers belonging to the HASE family. The hydrophobic modification improves electrolyte resistance significantly, making them the preferred choice in vitamin C serums, AHA formulations at low pH, mineral sunscreens, or any system where ionic load would destabilize a standard carbomer gel.



The specific role of associative thickeners in preventing creaming, sedimentation, and phase separation is covered in our dedicated article on rheology modifiers and emulsion stability.



3. Mineral-origin rheology modifiers



Mineral thickeners derive their rheological effect from physical colloidal networks rather than polymer chains, giving them a distinctive combination of high yield stress, good thixotropy, and long-term stability.



Bentonite and hectorite are swelling clays that form gel networks through electrostatic platelet interactions in aqueous systems. They deliver strong thixotropy and effective pigment suspension, making them the standard choice in face masks, mineral foundations, and any emulsion with a high dispersed solid load.



Laponite is a synthetic layered silicate that produces exceptionally clear aqueous gels through edge-to-face electrostatic interactions between nanoplatelets — the so-called "house of cards" network. It is the preferred mineral option in transparent serums and leave-on products where clay opacity would be unacceptable.



Fumed silica builds its thickening network through hydrogen bonding between silanols on its particle surface. It is particularly relevant in anhydrous formulations — lipsticks, eye products, pressed powders — where polymer-based thickeners are ineffective, and in powder systems requiring anti-caking performance at very low loadings.



Natural Rheology modifiers for Cosmetics



Natural-origin rheology modifiers have moved from niche to mainstream as COSMOS certification, clean beauty positioning, and European microplastic restrictions reshape formulation priorities.



The most used options are xanthan gum, guar gum, sclerotium gum, hydroxyethyl cellulose (HEC) from plant-derived sources, and alginates. Each brings a distinct performance profile. Xanthan gum delivers strong shear-thinning behaviour and broad pH stability, making it the backbone of most natural gel formulations. Guar gum, being nonionic, is compatible with cationic conditioning agents — an advantage in rinse-off and hair care systems. Sclerotium gum, produced by fungal fermentation, produces smooth, skin-friendly gels with a sensory profile close to synthetic acrylics, and is increasingly used as a carbomer replacement in COSMOS-certified leave-on products. Plant-derived HEC builds straightforward viscosity in surfactant systems without ionic sensitivity. Alginates, extracted from brown seaweed, are primarily used in rinse-off masks and structured gel formats.



The trade-offs are real. Natural modifiers generally require higher use concentrations than carbomers to reach equivalent viscosity. Some, like xanthan at high loading, introduce a ropy or stringy skin feel. Clarity is another constraint: most natural polymers produce hazy to opaque gels, which limits their use in transparent serums. Microbial susceptibility and batch variability also add formulation complexity compared to synthetic alternatives.



Priority use cases are natural gels, COSMOS-certified leave-on creams and serums, and rinse-off products where biodegradability is a requirement.



Hydrophilic vs Lipophilic Rheology Modifiers: Which for Which System?



The polarity of the continuous phase is the first filter in any modifier selection decision. Using the wrong family in the wrong phase produces no thickening effect, regardless of concentration.



Hydrophilic modifiers — carbomers, cellulose derivatives, xanthan gum, and carrageenan — are designed for aqueous phases and oil-in-water emulsions. They dissolve or swell in water, building viscosity through chain entanglement, associative networking, or ionic swelling. They are ineffective in anhydrous or water-in-oil systems.



Lipophilic and structuring modifiers handle the inverse cases. Organically modified clays (bentone, hectorite), hydrophobic fumed silica, waxes, fatty alcohols, and castor derivatives structure oil phases, anhydrous formulas, and water-in-oil emulsions. At low loadings, hydrophobic fumed silica prevents sedimentation and controls flow in lipsticks and pressed powders without altering colour or texture perception.



Key selection criteria for formulators



pH and neutralization



Carbomers and HASE polymers are supplied in acid form and must be neutralized to develop viscosity. This adds a manufacturing step and restricts use below pH 4 — a hard constraint for AHA, vitamin C, or low-pH preservative systems. Xanthan gum, guar, and most cellulose derivatives build viscosity across a wide pH range without neutralization, which simplifies manufacturing and opens up acidic formulation space.



Electrolyte tolerance



Electrolyte resistance is one of the most critical and frequently underestimated selection criteria. Standard carbomers lose viscosity rapidly in the presence of salts. Xanthan gum and carboxymethyl cellulose offer higher electrolyte resistance but at a sensory cost. In formulations with high ionic load — mineral actives, preservation systems, electrolyte-rich actives — associative acrylate crosspolymers or natural polysaccharides are the practical default.



Aqueous vs. anhydrous systems



Hydrophilic modifiers — carbomers, xanthan, HEC — are designed for aqueous phases. Structuring the oil phase or formulating anhydrous products requires different tools: waxes, fatty alcohols, organically modified clays, or hydrophobic fumed silica. The polarity of the continuous phase is the first filter in any selection decision.



Sensory profile



The modifier choice directly shapes the consumer's tactile experience. Carbomers produce a clean, cushioned, non-tacky skin feel. Polysaccharides can introduce a long, stringy flow at higher loading that reads as heavy or gel-like. Mineral systems like Laponite produce a lighter, drier, more mineral finish. Research using neurosensory consumer testing — including prosody analysis and dynamic brain activity measurement — has confirmed that rheological modifier choice produces distinct and measurable emotional responses. Matching the modifier to the sensory brief is as important as matching it to technical performance.



Sustainability and regulatory constraints



The transition toward bio-derived thickeners is reshaping formulation choices globally. Natural thickeners held approximately 42.5% of the cosmetic thickener market in 2025, marking a crossover point as naturally derived options continue to gain ground. COSMOS and Ecocert certification, REACH microplastic restrictions, and clean beauty positioning are progressively constraining the eligible thickener pool — particularly in European markets for both leave-on and rinse-off product categories.



Application by product type



Creams and lotions require stable viscosity in emulsified systems, resistance to thermal cycling, and a pleasant after-feel. Carbomers dominate in classic oil-in-water emulsions. For certified natural positioning, sclerotium gum and xanthan combinations are the most established alternatives.



Serums and lightweight fluids demand clarity and a non-tacky finish. Carbomers and Laponite are the main options for transparent, high-active serums. Electrolyte-compatible acrylate crosspolymers are preferred in vitamin C or AHA formulations at low pH.



Shampoos and rinse-off hair care operate in anionic surfactant systems where carbomers underperform. Carbomers and xanthan gum are the workhorses for sulfate-based systems. For sulfate-free and EO-free natural formulations, guar-xanthan synergy delivers the right combination of shear-thinning flow and yield stress.



Colour cosmetics — foundations, mascaras, lip products — require modifiers that handle high pigment loads, resist separation on storage, and deliver precise application rheology. Bentonite, hectorite, and fumed silica serve the mineral structuring role; carbomers and hydrocolloides structure the aqueous phase of fluid foundations.



Anhydrous and powder systems — lipsticks, balms, pressed powders — rely on waxes, fatty alcohols, and mineral materials. Fumed silica at low loadings controls flow and prevents caking without altering colour or texture perception.



Face masks leverage the thixotropic performance of clays, which build a structured gel at rest but flow on application. Carrageenan and xanthan serve water-wash and peel-off formats where clay opacity is undesirable.



FAQ



What is a rheology modifier in cosmetics?



An ingredient that changes how a formula flows: it thickens, suspends particles, stabilises emulsions and shapes the sensory on application.



Which rheology modifier works in high-salt or surfactant formulas?



Natural gums, cellulose derivatives and clays tolerate electrolytes well. Carbomers lose viscosity with salt.



What can replace carbomer?



Xanthan or sclerotium gum, cellulose derivatives or clays, often in blends. See our carbomer alternatives guide.



Which thickener is best for anhydrous formulas?



Organoclays such as hectorite and fumed silica, because they build structure in oils.



Summary



Rheology modifier selection is a system decision, not an ingredient decision. The polarity of the matrix, the pH, the ionic load, the processing constraints, the sensory target, and the sustainability brief all constrain the viable options before a single bench test is run. Understanding the mechanism behind each family — chain entanglement, associative networking, mineral hydrogen bonding — is what allows formulators to narrow the field quickly and reach a stable, consumer-validated formula with fewer reformulation cycles.


Browse rheology modifiers in our cosmetics catalogue

Need a thickener for your base? 

Rheology Modifiers in Cosmetics: Applications, Natural Options and How to Select


TL;DR : What Chemical Distributors Actually Do



The standard definition of a chemical distributor focuses on logistics: storing, handling, and delivering chemical substances to end users. This framing, while accurate, is increasingly insufficient. In the specialty chemicals sector — where active ingredients, polymer additives, cosmetic actives, and pharmaceutical excipients are subject to complex regulatory frameworks, demanding application requirements, and fast-moving reformulation cycles — the distributor's role has become substantially more sophisticated. A distributor positioned between a global chemical manufacturer and a regional customer base does not merely relay molecules. It translates technical knowledge, absorbs regulatory complexity, de-risks formulation decisions, and often co-develops solutions that neither the producer nor the end user could develop alone. Research published in the Journal of Operations Management (Selviaridis, 2025) confirms that intermediaries in supply networks create value precisely by addressing "shortfalls in the capabilities that buyers and suppliers must have to access each other's knowledge for innovation purposes." This framing applies directly to specialty chemical distribution, where the knowledge gap between a global producer and an SME formulator is frequently substantial





Technical Expertise as the Core Differentiator



The most consequential shift in specialty chemical distribution over the past decade is the move from transactional to consultative selling. A 2018 Boston Consulting Group white paper on specialty chemical distributors identified application support and formulation co-development as the primary axes on which leading distributors differentiate from pure logistics operators. Customers increasingly expect their distributor to understand their process chemistry, not just their delivery address.



This expertise takes several concrete forms:




Formulation support and application labs. Distributors operating in personal care, coatings, food, or rubber segments maintain laboratory infrastructure that allows customers to test new ingredients, troubleshoot existing formulations, and validate performance claims before committing to full-scale production. This is especially relevant for SME customers who lack in-house R&amp;D capacity.



On-site technical assistance. In industrial rubber compounding, for example, the conversion of liquid ingredients into dry liquid powders addresses persistent handling, dosing, and safety challenges directly on the factory floor — a level of intervention that goes well beyond conventional supply chain services.



Portfolio curation. Rather than offering undifferentiated access to thousands of raw materials, specialized distributors curate principal portfolios to minimize overlap and maximize complementarity. This enables deeper application-specific knowledge per category, allowing technical sales teams to act as formulation advisors rather than catalogue representatives.




Regulatory Navigation: A Structural Value Driver



The regulatory environment governing chemical substances in the EU and globally has grown considerably more complex since the entry into force of REACH (Regulation EC No 1907/2006). Under REACH, distributors bear a defined duty to communicate safety information along the supply chain — passing Safety Data Sheets downstream and relaying downstream use information back to registrants. This is not a passive administrative function; it requires active monitoring of Substances of Very High Concern (SVHC) candidate lists, interpretation of exposure scenarios, and coordination between chemical producers and their industrial customers.



For manufacturers working with dozens or hundreds of raw materials across multiple jurisdictions, the compliance burden is significant. A distributor with dedicated regulatory expertise — managing REACH, CLP labelling, GHS classification, food-contact compliance, pharmacopoeial standards, or cosmetics regulation depending on the sector — removes a structural burden from the customer's operational model. According to the ICTA (International Chemical Trade Association), regulatory compliance support is now one of the most cited rationales for outsourcing chemical procurement to specialist distributors, alongside blending, formulation, and repackaging services.



This compliance function has become a competitive moat. As specialty chemical market research (Research and Markets, 2024) notes, "proficiency in REACH, CLP, TSCA, GMP, and labelling compliance has become a core differentiator" for distributors serving sectors such as pharmaceuticals, personal care, and food ingredients.



Supply Chain Resilience and Multi-Sourcing



The COVID-19 pandemic, combined with subsequent geopolitical disruptions, exposed the fragility of single-source procurement strategies in chemical supply chains. A systematic literature review published in the Journal of Business &amp; Industrial Marketing (Emerald Publishing, 2024) on resilient B2B chemical supply chains highlights the increasing importance of redundancy, regional diversification, and information-sharing capabilities for supply continuity.



Distributors structured around multi-principal sourcing strategies — maintaining relationships with multiple producers of equivalent chemistries across different geographies — provide customers with a structural buffer against supply disruption. This is particularly valuable in specialty segments where switching between suppliers requires regulatory re-qualification, stability testing, or reformulation.



The distributor's aggregation function also generates economies of scope that individual customers cannot replicate: by pooling demand across hundreds of accounts, a distributor can negotiate access to materials in volumes, delivery formats, or lead times that would be commercially inaccessible to smaller buyers acting independently.



Knowledge Transfer Across the Value Chain



Research on knowledge sharing in supply chain networks (MDPI, Logistics, 2022) identifies knowledge transfer as a primary performance driver for supply chain participants. In the specialty chemicals context, this transfer is bidirectional: distributors carry application knowledge from suppliers to formulators, and they carry emerging formulation challenges and regulatory signals from customers back to producers — enabling more targeted product development at the manufacturing level.



This mediating position is commercially significant. A distributor that understands both a producer's technical roadmap and a customer's formulation pipeline can anticipate compatibility issues, propose ingredient substitutions ahead of regulatory deadlines, and accelerate time-to-market for new products. In sectors like adaptive cosmetics — where the interplay between ingredient sourcing, regulatory compliance, and sustainability claims requires simultaneous expertise across multiple dimensions of the value chain — this integrated knowledge function is increasingly indispensable.



Sustainability and Substitution Pipelines



Environmental regulation and ESG commitments are reshaping raw material portfolios across virtually all chemical-consuming industries. Distributors are uniquely positioned to facilitate the transition to greener chemistries because they hold relationships on both sides of the substitution decision: access to alternative chemistries from producers, and formulation knowledge of the performance benchmarks customers need to match.



The technical validation of bio-based, PFAS-free, or low-VOC alternatives — demonstrating equivalent performance to incumbent materials — is a service that requires both laboratory infrastructure and application expertise. Market analysis consistently identifies sustainability-driven substitution as one of the primary growth vectors in specialty distribution, with distributors acting as solution architects rather than passive product conduits.



What This Means for Industrial Buyers



For procurement and formulation teams evaluating distribution partnerships, the relevant question is no longer simply which distributor can deliver a given product at the best price. The more strategic question is which partner brings a combination of regulatory intelligence, formulation expertise, supply resilience, and sustainability advisory capability that creates tangible value across the product development and procurement lifecycle.



In a market where chemical complexity continues to increase and regulatory requirements continue to tighten, the distributor who can translate that complexity into actionable formulation guidance — and absorb the compliance burden that would otherwise fall on the customer — is performing a function that is genuinely irreplaceable by direct sourcing models.


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How Chemical Distributors Add Value Beyond Logistics

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