What it is
Polyhydroxystearic acid is a polymer (homopolymer) of hydroxystearic acid that acts as a dispersing agent in cosmetics. It is used in inorganic sunscreens based on titanium dioxide or zinc oxide, and in color cosmetics, to coat and distribute the particles evenly across the skin. By improving how the mineral particles are wetted and spread, it can help even out the formula and reduce the visible white cast typical of mineral sunscreens.
Safety & warnings
As a fatty-acid-derived polymer used to coat and disperse pigments, polyhydroxystearic acid is typically a well-tolerated formulation aid rather than an active. It is widely used in mineral sunscreens, foundations, and SPF lip products, where its role is to keep particles evenly suspended.
Origin & sourcing
It is made by polymerizing hydroxystearic acid, most commonly 12-hydroxystearic acid. That building block is itself obtained from castor oil, whose main fatty acid, ricinoleic acid, is hydrogenated and saponified to yield 12-hydroxystearic acid.
Questions everyone asks
Why is polyhydroxystearic acid in mineral sunscreen?
It coats and disperses the mineral UV filters like titanium dioxide and zinc oxide so they spread evenly and leave less white cast.
Is it natural?
It is a polymer made from hydroxystearic acid, which is commonly derived from castor oil, then processed into the cosmetic ingredient.
Does it act as a sunscreen filter itself?
No. It does not absorb UV; it helps distribute the mineral filters that do the protecting.