melanine

Melanine, commonly spelled melanin in English, is a class of pigments produced by specialized cells called melanocytes, primarily in the skin, hair follicles, and eyes of humans and other mammals. Biochemically, melanin is synthesized in melanosomes within melanocytes through melanogenesis, beginning with the amino acid tyrosine and the enzyme tyrosinase; the two major forms are eumelanin (brown-black) and pheomelanin (red-yellow). Genetic and environmental factors influence production: tyrosinase activity and MITF regulate enzyme levels; MC1R variants are associated with red hair and lighter skin; ultraviolet exposure increases enzyme activity and melanosome transfer to keratinocytes as a photoprotective response.

Body distribution and function: melanin absorbs ultraviolet light, dissipates energy as heat, and helps protect skin against DNA damage; the amount and distribution of melanin determine color in skin, hair, and eyes. Melanin is produced in melanocytes and transferred as melanosomes to neighboring keratinocytes; darker skin generally contains more eumelanin, and the shape and size of melanosomes influence appearance.

Neuromelanin, a related pigment in brain regions such as the substantia nigra, is accumulated with age; its precise function is not fully understood, but it may bind metals and protect neurons from oxidative stress.

Clinically, disorders of melanin production include hypopigmentation conditions such as albinism and vitiligo, and hyperpigmentation conditions such as melasma and post-inflammatory hyperpigmentation. Melanin biology is a topic of ongoing research, spanning evolutionary biology, dermatology, and neuroscience.