: any of various black, dark brown, reddish brown, or yellow pigments of animal or plant structures (as skin, hair, the choroid, or a raw potato when exposed to air); especially: any of numerous animal pigments that are essentially polymeric derivatives of indole formed by enzymatic modification of tyrosine
Any of several organic compounds, dark biological pigments that give coloration (shades of yellow to brown) to skin, hair, feathers, scales, eyes, and some internal tissues, notably the substantia nigra in the brain. In humans, melanins help protect the skin against the damaging effects of ultraviolet radiation, but melanoma may arise from cells that produce it. The amount in the skin depends on both genetic and environmental factors. Melanin is produced from the amino acidtyrosine; albinos lack the enzyme that catalyzes that reaction (seealbinism).