Melanin

Melanin is a group of pigments produced by specialized cells called melanocytes, which are located in the epidermis, as well as in the hair follicles, iris, and some parts of the brain. Melanin determines the color of skin, hair, and eyes and contributes to photoprotection.

Two main forms: eumelanin (brown to black) and pheomelanin (yellow to red). The relative amounts determine color. Melanin is synthesized in melanosomes within melanocytes from the amino acid tyrosine, via a pathway catalyzed by the enzyme tyrosinase, producing DOPA and dopaquinone and leading to eumelanin or pheomelanin depending on enzymes and signaling.

Melanosomes are transferred from melanocytes to keratinocytes, where they accumulate above the nucleus to shield DNA from ultraviolet radiation. Exposure to UV light stimulates melanin production by increasing eumelanin synthesis, resulting in tanning.

Genetic factors influence melanin production and type; notable genes include MC1R. Variation in melanin levels is common among populations and reflects evolutionary adaptation to ultraviolet radiation. Melanin can also be found in ocular tissues and is involved in vision.

Clinical notes include conditions such as albinism and vitiligo, and melanoma. Albinism refers to reduced or absent melanin due to enzyme deficiencies or other genetic defects. Vitiligo involves loss of melanocytes in patches, and melanoma is a malignant tumor of melanocytes. Melanin biology has implications in dermatology, ophthalmology, and anthropology.