What it is
Methyl Trimethicone is a very light, volatile branched silicone (chemically 1,1,1,3,5,5,5-heptamethyl-3-(trimethylsilyloxy)trisiloxane). It evaporates from the skin rather than penetrating it, leaving a smooth, dry, non-greasy finish, and it dries even faster than the commonly used cyclopentasiloxane. In formulas it acts as an emollient and solvent, helping spread other ingredients evenly and giving sunscreens and makeup a quick-setting, weightless feel. It is a sensory and carrier ingredient rather than an active.
Safety & warnings
As a volatile silicone that largely evaporates and does not penetrate the skin, Methyl Trimethicone is generally well tolerated and is used in a wide range of facial sunscreens and makeup where a light finish is wanted. It is not associated with notable irritation or sensitization for most users, though anyone with very reactive skin can patch test a new product.
Origin & sourcing
It is a synthetic silicone fluid. It is produced commercially as a low-viscosity branched siloxane and is sold, for example, by Shin-Etsu under the trade name TMF-1.5, with a viscosity of about 1.5 centistokes, for use in skin care, hair care, makeup and suncare.
Questions everyone asks
What does Methyl Trimethicone do in sunscreen?
It is a light, volatile silicone that helps the product spread and dries quickly to a smooth, non-greasy finish.
Does it leave a greasy or heavy feel?
No. It evaporates instead of sinking in, leaving a dry, weightless touch, drying even faster than cyclopentasiloxane.
Is Methyl Trimethicone the same as cyclomethicone?
It is a different volatile silicone used for similar light-feel purposes; it is branched and evaporates very quickly.