Aluminum Stearate

Aluminum stearate is a fatty-acid metal salt used mainly as a thickener/anti-caking agent in powders and some topical formulations, typically at low concentrations (often ~0.5–5%). It is generally considered low-irritant and not a common sensitizer in patch-testing, but as an insoluble particulate it can contribute to mild mechanical/occlusive irritation in highly reactive or eczematous skin, especially with repeated leave-on exposure. Given sensitive-skin safety priorities, I rate it as gentle rather than inert. Safety Notes: In commercial skincare, aluminum stearate is typically used as a low-level suspending agent/viscosity modifier and opacifier in creams, lotions, sunscreens, and some cleansers, where it is often present around 0.05–1%. Higher consumer-available levels are observed in very waxy anhydrous systems (balms, sticks, barrier ointments, some makeup-adjacent skincare) where it functions as a gellant/structurant and can reach roughly 3–8% depending on the oil/wax load and desired payoff. It is more commonly found at higher percentages in leave-on anhydrous formats than in rinse-off products, and no specific EU/FDA cosmetic concentration limit is generally set beyond overall safety substantiation and impurity control.