Polystyrene
INCI: POLYSTYRENE
Reviewed by Rosie · Last updated 14 Aug 2026
A film-forming polymer with emerging safety considerations for topical use
Best For Skin Types
All
Usage Frequency
As directed
What Is Polystyrene?
Polystyrene is a synthetic polymer derived from petroleum. In skincare formulations, it functions as a film former — a ingredient that creates a thin, continuous layer across the skin surface. This physical barrier can help retain moisture and provide a smooth texture to products.
The ingredient is used primarily in cosmetics for its ability to provide structure and adhesion to formulations, though it appears in a relatively small proportion of skincare products compared to other film-forming agents.
How It Works
Polystyrene works by forming a continuous polymeric film across the skin. This physical layer sits on the surface, creating a barrier that can help minimise moisture evaporation. The polymer chains link together to create a cohesive network rather than penetrating the skin.
Clinical Evidence & References
Recent research has raised questions about the safety profile of polystyrene when used topically. In-vitro and ex-vivo studies suggest that fragmented polystyrene particles, particularly those smaller than 2 micrometres, may penetrate into deeper skin layers and trigger inflammatory responses in skin cells. Particle penetration has been observed within one hour of exposure in laboratory models.
However, it is important to note that most existing evidence comes from controlled laboratory settings and animal models, and the practical significance of these findings for routine cosmetic use remains unclear. The concentration at which polystyrene appears in skincare products and the extent to which it fragments during storage and application require further investigation.
How to Use
If using a product containing polystyrene, apply as directed by the formulation. There is no evidence that increased frequency or concentration improves efficacy. If you have concerns about microplastic exposure from cosmetics, you may prefer formulations with alternative film-forming agents such as acrylates or plant-derived polymers.
Safety & Precautions
Frequently Asked Questions
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