Polyhydroxystearic Acid

Polyhydroxystearic Acid is a high–molecular weight fatty acid polymer used mainly as a dispersant/thickener in makeup and mineral sunscreen, typically at low percentages. Available safety assessments and its non-volatile, non-acidic, non-surfactant nature suggest low irritation potential in routine use, with reactions being uncommon and more likely related to individual intolerance in very compromised skin. Given the sensitive-skin context and limited large-scale irritation data compared with more ubiquitous emollients, I score it as very gentle rather than inert. Safety Notes: Polyhydroxystearic Acid is used primarily as a dispersant/wetting agent and stabilizer in anhydrous or low-water systems (especially mineral sunscreens, color cosmetics, and silicone/oil-based serums), where it can appear at very low levels (~0.05–0.3%) simply to aid pigment dispersion and improve feel. In higher-load zinc oxide/titanium dioxide sunscreens, foundations, and sticks, commercial OTC formulas commonly use ~1–5% and can reach about 8–10% in high-pigment/high-mineral, consumer-available products to maintain uniform dispersion and prevent settling (higher levels are uncommon due to viscosity/drag and sensorial limits). It is generally a leave-on ingredient; rinse-off products tend to sit at the low end when used at all.