What it is
Polydiethylsiloxane is a silicone polymer in which the silicon backbone carries ethyl side groups rather than the methyl groups of the more common dimethicone. This structural difference gives it a distinctive sensory profile, contributing slip, spreadability, and a soft skin feel in formulations. In sunscreens it helps deliver a smooth application and an even, non-greasy finish.
Safety & warnings
Silicone fluids of this type are generally well tolerated, chemically inert on skin, and have a low likelihood of irritation or sensitization. They are not associated with the fragrance-allergen or comedogenic-oil concerns that apply to many botanical ingredients.
Origin & sourcing
Synthetic; an industrially manufactured silicone polymer.
Questions everyone asks
How is this different from dimethicone?
It carries ethyl side groups instead of methyl groups on the silicone backbone, which gives it a somewhat different slip and skin feel.
What does it do in sunscreen?
It acts as an emollient and conditioning silicone that improves spreadability and gives a smooth, lightweight finish.