Dimethicone

Dimethicone is a silicone polymer. In cosmetics, it acts as an emollient, softening the skin’s surface and leaving it smooth to the touch. It is not listed among prohibited or restricted substances in the annexes to Regulation (EC) No 1223/2009. The silicones subject to European restrictions belong to a different family: the cyclic siloxanes D4, D5 and D6.

Two questions need separating: what has been measured on the skin, and which silicones European law restricts.

What it does inside the product

The European CosIng database assigns dimethicone four functions: antifoaming, emollient, skin conditioning and skin protecting.

The first concerns foam formation in the formula. The other three describe its role on the skin. The last has a regulatory counterpart in the United States: the Food and Drug Administration’s 21 CFR 347.10 lists dimethicone as a permitted skin protectant active ingredient at 1% to 30%.

What has been measured on the skin

The image of a film on the skin often prompts the question: does silicone suffocate it? Looking at what researchers measured is more useful.

The Cosmetic Ingredient Review is the US expert panel that reassesses cosmetic ingredient safety, with conclusions relating to the American market. Its report of 19 April 2022 describes two penetration studies. In the first, human abdominal skin samples mounted in Franz diffusion cells were exposed for 96 hours. Measured flow through the skin was 0.2 and 0.3 nanograms per square centimetre per hour, depending on the applied viscosity. In the second, human stratum corneum samples treated with four dimethicone viscosities were examined using thermal analysis, X-ray diffraction, polarised light microscopy and transmission electron microscopy. The authors concluded that dimethicone left the liquid-crystalline structure of the upper epidermal layer intact and therefore most likely remained outside the skin barrier.

The molecule’s structure helps explain this. Dimethicone is a linear polymer, a chain of repeating units, and viscosity increases with chain length. The same report notes that fluids of 100 and 350 centistokes are commonly used in cosmetics.

The report of 19 April 2022 concludes that dimethicone and the other twenty-nine polymers assessed are safe in cosmetics under the uses and concentrations described, provided the formula is made to be non-irritating. It also states an exception: the available data were considered insufficient for products that may be inhaled during airbrush application.

Cyclic siloxanes belong to a different family

The European restrictions concern three specific molecules: octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). Their INCI names are Cyclotetrasiloxane, Cyclopentasiloxane and Cyclohexasiloxane. The prefix cyclo signals the difference: they are closed rings, individual molecules of fixed size. Dimethicone is a linear chain of variable length.

Commission Regulation (EU) 2024/1328 amended entry 70 of Annex XVII to REACH, the chemicals regulation. It prohibits placing these three molecules on the market at concentrations of 0.1% by weight or more after 6 June 2026, including when they occur as constituents of other substances or in mixtures. For rinse-off cosmetics, the D4 and D5 limit has applied since 31 January 2020; for other cosmetics, the date is 6 June 2027.

The regulation’s recitals explain the environmental reason: the three molecules are identified as substances of very high concern, very persistent and very bioaccumulative, with D4 also classified as persistent, bioaccumulative and toxic. D4 also has its own entry, 1388, in Annex II to Regulation (EC) No 1223/2009, the list of substances prohibited in cosmetics.

What European law says about dimethicone

CosIng lists dimethicone as active, with CAS numbers 63148-62-9, 9006-65-9 and 9016-00-6. Its restrictions field is empty, no Scientific Committee on Consumer Safety opinion is linked to the entry, and dimethicone does not appear among prohibited or restricted substances in the annexes to Regulation (EC) No 1223/2009.

Read that statement precisely: it describes a list’s status at a particular date, which can be checked in CosIng. A regulatory list tells you what is permitted on the market; how one person’s skin tolerates a product is a separate question.

Where to find it on the label

It appears as Dimethicone. You may see related names such as Cetyl Dimethicone or Amodimethicone: these are derivative polymers, each with its own name and profile.

Ingredients above 1% follow descending order; those below that threshold may appear in any order. Our guide to reading an INCI list explains this in full. Use the INCI analyser to explore a complete label.

Sources: CosIng, European Commission (Dimethicone, Cyclopentasiloxane, Cyclohexasiloxane and Cyclomethicone entries). Commission Regulation (EU) 2024/1328, entry 70 of Annex XVII to Regulation (EC) No 1907/2006. Cosmetic Ingredient Review, Amended Safety Assessment of Dimethicone, Methicone, and Substituted-Methicone Polymers as Used in Cosmetics, Final Amended Report, 19 April 2022. Code of Federal Regulations, Title 21, section 347.10.