What it is
This ingredient is a copolymer formed by reacting PEG-8 with saturated methylenediphenyl diisocyanate (SMDI). In formulations it builds a flexible film on the skin surface that helps deposit and hold pigments and other actives in place, and it contributes to the body and texture of the product. It is commonly found in mineral and tinted sunscreens where even, durable coverage of pigments is desired.
Safety & warnings
Generally regarded as well tolerated in cosmetic use, with a low expected rate of irritation or sensitization. As a high-molecular-weight polymer it is not appreciably absorbed through intact skin.
Origin & sourcing
Synthetic; manufactured by polymerizing PEG-8 (a polyethylene glycol) with a saturated diisocyanate building block.
Questions everyone asks
What does PEG-8/SMDI Copolymer do in a sunscreen?
It acts mainly as a film former and thickener, helping the product spread evenly and helping pigments and other ingredients stay in place on the skin.
Is it a UV filter?
No. It does not absorb or scatter ultraviolet light; it is a formulation polymer that supports texture and film formation.