Melanin

Melanin is the name of a group of compounds found within the body which serve primarily as pigments. It is found in most humanoids and animals, though some, such as Andorians, are colored by a different group of pigments. Melanin pigments determine the color of skin, hair and the iris of the eye. Melanin can also be found in areas of the body other than the skin, particularly the adrenal gland and the brainstem, though it is unclear what the function of these particular compounds may be.

The most common melanin pigment is eumelanin, a brown-black pigment which is responsible for making hair black, brunette, blonde or grey. People with dark skin have more dermal eumelanin than those with paler skin, and it is the natural variations found in eumelanin which causes the differing skin tones found between races. Another common melanin pigment is pheomelanin. This is a red-brown pigment and is responsible for causing red hair. It also causes the pinkness found in lips, nipples and parts of the genitalia. Additionally, small concentrations of pheomelanin can become visibly evident on the skin in the form of freckles.

As well as coloring skin, melanin also works to protect it by absorbing the majority of harmful UV radiation it is exposed to by sunlight, converting it into heat at levels which cause no damage to the body. Melanocytes, the cells which produce melanin, increase their rates of melanin production in response to higher levels of sunlight in order to process the extra radiation the skin is being exposed to. This increased production causes the darkening of skin (a sun tan) after a few hours.

The partial or total lack of melanin pigments results in a condition called albinism. People with albinism usually have white or pale yellow skin, hair and irises. The opposite, the over abundance of melanin pigments, is known as melanism and causes jet black skin, hair and irises. Melanin has the capacity to become carcinogenic after prolonged exposure to sunlight, and can be a contributing factor to the formation of a type of skin cancer called melanoma.