What it is
PEG/PPG-18/18 dimethicone is a dimethicone backbone modified with polyethylene-glycol and polypropylene-glycol side chains, making it a water-dispersible silicone surfactant. In sunscreens it is commonly used to emulsify water-in-silicone systems and to give a light, silky, non-greasy skin feel. It improves spreadability and helps stabilize emulsions.
Safety & warnings
This silicone copolymer is generally well tolerated and non-sensitizing in typical cosmetic use. It is not a recognized fragrance allergen and is not considered notably comedogenic, though as with any emulsifier the complete formulation governs overall skin feel and tolerability.
Origin & sourcing
Synthetic. It is a silicone-polyether copolymer manufactured by attaching PEG and PPG groups to a dimethicone polymer.
Questions everyone asks
Why is PEG/PPG-18/18 dimethicone used in sunscreen?
It works as a silicone-based emulsifier that stabilizes water-in-silicone formulas and gives a light, silky, fast-spreading feel.
Does it leave a greasy residue?
Generally no. Silicone-polyether emulsifiers like this one are chosen partly because they help formulas feel light and non-greasy on the skin.