melanocyte

Melanocytes are pigment-producing cells located in the epidermis, hair follicles, and certain other tissues. They are derived from neural crest cells and reside in the basal layer of the epidermis, extending dendritic processes that contact keratinocytes.

Melanin synthesis occurs within melanosomes inside melanocytes. The enzyme tyrosinase initiates the biochemical pathway from tyrosine to DOPA to dopaquinone, producing the pigments eumelanin and pheomelanin. Synthesis and pigment production are influenced by genetics, age, hormones, and ultraviolet exposure. Melanosomes are transferred to keratinocytes via the melanocyte dendrites, distributing pigment that contributes to skin and hair color.

The primary function of melanocytes is photoprotection. Melanin absorbs and dissipates ultraviolet radiation, helping to reduce DNA damage in skin cells. The amount, type, and distribution of melanin determine individual skin and hair color, and variations in distribution underlie tanning and freckles.

Clinical relevance includes several conditions affecting melanocytes or melanin production. Albinism involves reduced or absent melanin due to defective synthesis. Vitiligo is characterized by the autoimmune loss of melanocytes, leading to depigmented patches. Melasma is a hyperpigmented condition due to increased melanin production in the skin. Melanocytes can also give rise to melanoma, a malignant tumor. In addition to the skin, melanocytes are present in other tissues such as the uveal tract of the eye and play roles in related pigmentation processes.