Silicones in Cosmetics: Safety Depends on Which One, and How It Is Used

“Silicone” on a cosmetic label describes a broad chemical family, which makes blanket safety claims unusually unhelpful. Volatile cyclic siloxanes, including D4, D5 and D6, are small molecules used to create fast spread, slip and a dry-down effect. Larger linear polymers such as dimethicone remain on skin or hair more readily and can provide conditioning, shine, film formation and a smoother feel. Those differences shape exposure, performance and environmental questions.

D4 and D5 illustrate why the distinction matters. The European Chemicals Agency says D4 has a harmonised EU classification as suspected of damaging fertility and has been placed on the Cosmetics Regulation prohibited list because of that reproductive toxicity classification. D5 has prompted a different set of concerns, focused heavily on persistence and bioaccumulation in the environment. The European Commission’s Scientific Committee on Consumer Safety found D5 safe at reported cosmetic concentrations, except in hair styling aerosols and sun care sprays, where inhalation exposure could raise concern. Its 2016 opinion also advised minimizing D4 as an impurity in D5. European Chemicals Agency SCCS opinion on D5

Higher molecular weight dimethicone and methicone polymers have a separate consumer safety record. In its 2022 reassessment of 30 related ingredients, the Cosmetic Ingredient Review concluded they were safe as used when formulated to be non-irritating. The panel found the available evidence insufficient to determine safety for products incidentally inhaled through airbrush application. Product format therefore remains part of the answer, even for silicone polymers with a comparatively reassuring topical-use assessment. Cosmetic Ingredient Review’s safety assessment

Concentration is becoming a practical formulation constraint in Europe. The EU’s 2024 REACH amendment limits D4, D5 and D6 to 0.1% by weight in mixtures from June 6, 2026, with specific transition provisions for cosmetics. D4 and D5 have already faced the 0.1% wash-off cosmetics limit since January 31, 2020. The broader limit reaches leave-on and other non-wash-off cosmetics on June 6, 2027. The rule targets the small cyclic siloxanes, not every silicone polymer, a distinction obscured when “silicone-free” is treated as a single environmental claim. Commission Regulation (EU) 2024/1328

Replacing D5 is a formulation exercise, not an ingredient-list exercise. Volatile alkanes, hydrocarbons, esters and ethers can supply parts of its sensory profile, yet each changes the system around it. A substitute can alter pigment wetting, sunscreen-active solubility, fragrance lift, hair conditioning, transfer resistance, oxidation stability or the final skin feel. Several ingredients, at carefully chosen levels, may be needed to reproduce the spread and dry touch once supplied by a single volatile silicone. Cosmetics & Toiletries

Sustainability claims need the same specificity. An alkane may be fossil derived, or made from renewable feedstocks; an ester may be plant derived while still raising questions about feedstock sourcing, processing energy and end-of-life behavior. Certification systems can set useful sourcing and processing rules, yet a natural or organic designation does not establish lower toxicological or environmental impact for every finished formula. COSMOS, for example, is a standard for sourcing, processing, composition and environmental management, not a universal comparative risk score. COSMOS-standard

For a leave-on product intended for the EU market, the immediate question is concrete: can its D4, D5 and D6 content meet the 0.1% mixture threshold by June 6, 2027, while preserving the formula’s performance and documenting the environmental case for whatever replaces it?