Aluminum hydroxide is used as a skin protectant and opacifier (to reduce transparency) in cosmetics. It can be used in many products such as foundations, lipsticks, and moisturizers.
Many sunscreens use aluminum hydroxide as a film on the titanium dioxide to prevent it from clumping so that it can be applied evenly. In addition to preventing it from penetrating the skin, it can also form a refractive layer to help the skin reflect UV rays.