Melanin
Melanin is a pigment that affects skin, eye, and hair colour in humans and other mammals. It is produced by melanocytes, which are found in the bottom layer of the skin's epidermis. Some individual animals and humans have no or very little melanin in their bodies, which condition is known as albinism. Melanin helps protect the skin from damage caused by ultraviolet (UV) radiation from the sun. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed.People whose ancestors lived for long periods in the regions of the globe near the equator generally have more active melanocytes, and therefore larger quantities of melanin in their skins. This makes their skins dark brown or black and protects them against high levels of UV exposure. In areas of the globe closer to the poles, people have far less need for protection from ultraviolet radiation, so their skin is usually lighter in colour. This allows sunlight to stimulate vitamin D production.
Freckles and moless are formed where there is a greater concentration of melanin in the skin.
Albinism is a condition in which an animal (such as a human or a mouse) is incapable of producing melanin, and hence appears white with pink eyes.
See also carotene, human skin color, melanism