dimethicone
what it is
A silicone — a polymer built on a silicon-oxygen backbone, INCI name Dimethicone. It is inert and odourless, and it does not react with skin or with anything else in the formula.
why we use it
In cloud it provides slip and forms a light film that slows water loss without heaviness. In the sunscreen it helps the formula spread into a uniform layer — which is protection, not polish, because an uneven sunscreen film is an unreliable one.
where you'll find it
In cloud at 1.50%, and in our mineral sunscreen (SPF 50+ PA++++), in the silicones group (8.25% total). Per-ingredient percentages within the sunscreen groups are not yet published; the group totals are exact.
evidence
Strong evidence as an occlusive that reduces transepidermal water loss; it is recognised as a skin protectant in the US over-the-counter framework.
safety
Silicones attract three criticisms, so here they are. Suffocation: the film is permeable to water vapour, so it does not seal skin shut. Clogged pores: comedogenicity testing does not support this for dimethicone. Environment: the restricted silicones are the small cyclic ones, D4 and D5, in rinse-off products; dimethicone is a large, non-volatile polymer — persistent, but inert. We use it in small amounts, knowingly, and would rather explain the trade-off than dodge it.