eumelanin

Eumelanin is a type of melanin pigment produced by melanocytes, cells located in the epidermis, hair follicles, and the uveal tract of the eye. It forms brown to black pigment in skin, hair, and irises, and it is one of the main determinants of human coloration alongside pheomelanin. The production of eumelanin begins with the amino acid tyrosine, which is oxidized by the enzyme tyrosinase to DOPA and then to DOPAquinone. Enzymes TYRP1 (tyrosinase-related protein 1) and DCT (dopachrome tautomerase) act downstream to channel intermediates toward eumelanin rather than pheomelanin. The availability of thiols and other factors influences whether eumelanin or pheomelanin is formed.

Eumelanin is a high-molecular-weight, insoluble polymer that is deposited in melanosomes and transferred to keratinocytes. It absorbs ultraviolet and visible light broadly and provides photoprotection partly by quenching reactive species and dissipating absorbed energy as heat. Its chemical stability contributes to long-lasting pigmentation. Higher eumelanin content generally yields darker skin and hair colors and greater resistance to UV-induced DNA damage.

Clinically, variation in eumelanin content underlies racial and individual differences in skin, hair, and eye color. Defects in the eumelanin pathway, as in oculocutaneous albinism, reduce pigment production and lessen UV protection. Eumelanin continues to be studied for its role in protection against UV damage, its antioxidant properties, and its behavior as a photoprotective polymer.