Melanin i/ˈmɛlənɪn/ (Greek: μέλας, black) is a pigment that is ubiquitous in nature, being found in most organisms (spiders are one of the few groups in which it has not been detected). In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms. Most are derived from the amino acid tyrosine. Another common form of melanin is pheomelanin, a cysteine-containing red-brown polymer of benzothiazine units largely responsible for red hair and freckles. The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing debate among researchers in the field. (Synthetic molecules, also called "melanins", are derivatives of polyacetylene.)
The increased production of melanin in human skin is called melanogenesis. Production of melanin is induced by UVB-radiation simulated by DNA is also a photoprotectant, . The photochemical properties of melanin make it an excellent photoprotectant. This is because it efficiently absorbs harmful UV-radiation (ultraviolet) and transforms the energy into harmless heat. This occurs by means of a process called "ultrafast internal conversion". This property enables melanin to dissipate more than 99.9% of the absorbed UV radiation as heat (see photoprotection). This prevents the UVB radiation damageindirect DNA damage that is responsible for the formation of malignant melanoma and other skin cancers.