melaniin

Melanin, sometimes written melaniin, is a pigment produced by specialized skin cells called melanocytes, which reside in the epidermis, hair follicles, and parts of the eye. It is synthesized within organelles called melanosomes and transferred to keratinocytes, contributing to skin, hair, and iris color and helping protect tissues from ultraviolet radiation.

There are two main forms: eumelanin, which is brown to black, and pheomelanin, which is red to yellow. The balance between these forms determines an individual’s coloration and hair color; higher eumelanin yields darker skin and hair, while more pheomelanin can give lighter or reddish tones.

Biosynthesis begins with the amino acid tyrosine, converted by the enzyme tyrosinase to DOPA and then to dopaquinone. Pathways diverge to form eumelanin (via TYRP1 and DCT) or pheomelanin (involving cysteine). Production is regulated by genetic and hormonal signals, notably the MC1R receptor and the MITF transcription factor; ultraviolet exposure promotes synthesis, contributing to tanning.

Melanin is packaged in melanosomes within melanocytes and transferred to keratinocytes, where it accumulates around the nucleus to shield DNA from UV damage. Population differences reflect genetic variation; exposure to sunlight, age, and hormonal changes also modify pigmentation. Clinically, reduced pigment causes albinism; autoimmune destruction of melanocytes causes vitiligo; uneven pigmentation and dark spots are common hyperpigmentation disorders.

In the brain, there is neuromelanin in regions such as the substantia nigra and locus coeruleus. Its exact function is not fully understood, but it may be involved in metal binding and protection against oxidative stress; abnormal accumulation or loss is linked to certain neurodegenerative conditions.