Melanin // (Greek: μέλας - melas, "black, dark") is a broad term for a group of natural pigments found in most organisms (arachnids are one of the few groups in which it has not been detected). Melanin is a derivative of the amino acid tyrosine, however it is not itself made of amino acids and is not a protein. The pigment is produced in a specialized group of cells known as melanocytes.
There are three basic types of melanin: eumelanin, pheomelanin, and neuromelanin. The most common type is eumelanin, and is produced in 'black' and 'brown' subtypes. Pheomelanin is a cysteine-containing red-brown polymer of benzothiazine units largely responsible for red hair and freckles. Neuromelanin is found in the brain, though its function remains obscure.
The production of melanin is called melanogenesis. In the skin, melanogenesis occurs after exposure to UV radiation, causing the skin to visibly tan. Melanin is an effective absorber of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, melanin is thought to protect skin cells from UVB radiation damage, reducing the risk of cancer. Furthermore, though exposure to UV radiation is associated with increased risk of malignant melanoma, a cancer of the melanocytes, studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin, i.e. darker skin tone. Nonetheless, the relationship between skin pigmentation and photoprotection is still being clarified.