"Sunscreen works by combining organic and inorganic active ingredients." In sunscreen, some of the ingrediants scatter UV rays while some absorb it, releasing it as heat. The agents that scatter the UV rays are usually mirrored, while an example of something that absorbs rays is white zinc oxide, or the white lotion that lifeguards spread on their noses.

The diagram below shows the epidermis (the outer layer of the skin) and the dermis (the layer underneath the epidermis). These together make up our skin. Sunblock is applied to the outer layer of skin, the epidermis. There, it forms a white or clear protective layer. So, instead of penetrating the skin, as the UV rays are doing now, the rays are either absorbed into the sunblock layer or reflected by the sunblock.