Methyl Trimethicone
No meaningful concern for most people; irritation is possible but rare.
Also written as: Tetramethyl tetra(trimethylsiloxy)cyclotetrasiloxane blend
What it is
Methyl trimethicone is a low-viscosity branched silicone that evaporates from the skin after application, leaving a dry, powdery-smooth feel. Formulators use it as a lighter alternative to volatile cyclic silicones such as cyclopentasiloxane, since it is not one of the cyclic siloxanes restricted under REACH.
What it does well
Gives a light, dry finish and helps products spread
It thins heavy oils and pigments so a formula spreads easily, then evaporates so no oily film remains.
Moderate evidence
Where the EU stands
No specific restriction
Not listed in any annex of the Cosmetics Regulation. It is also not one of the three substances the REACH cyclic-siloxane restriction names: Annex XVII entry 70 covers D4, D5 and D6 by name and CAS number, and methyl trimethicone is a different substance. That entry does also catch the three as constituents of other substances at 0.1% or more by weight, so what it reaches in practice is siloxane residues in a raw material, not methyl trimethicone itself.
Regulation (EC) No 1223/2009 - no annex entry · source ↗
Sources (1)
Every link goes to the original: a journal, a PubMed record or an EU document.
- [1]Commission Regulation (EU) 2024/1328 amending Annex XVII to Regulation (EC) No 1907/2006 (REACH) as regards octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6)
EUR-Lex, European Union · 2024
Replaces REACH Annex XVII entry 70. The entry names exactly three substances - D4 (CAS 556-67-2), D5 (CAS 541-02-6) and D6 (CAS 540-97-6) - and bars placing them on the market on their own, as a constituent of other substances, or in mixtures at a concentration of 0.1% or more by weight after 6 June 2026, with cosmetic products other than wash-off derogated to 6 June 2027. Methyl trimethicone is none of the three. Checked 18 September 2026.
