Melanin is a term to refer to a group of pigments produced from the oxidation oftyrosine, followed by polymerization. It is produced by and stored in melanocytes or melanophores. The colours may vary and may be used as a basis for classifying melanin. There are three basic types of melanin: (1) eumelanin, (2) pheomelanin, and (3) neuromelanin.
Pheomelanin is comprised of benzothiazine units and contains sulfur. It is responsible for yellow and pink to red hues based on the amount present. In humans, this pigment occurs in relatively large amounts in lips, nipples, vagina, and glans penis. It also accounts for the red pigmentation of hair. When present in the skin in considerable amount it would cause pinkish hue to the skin. Thus, redheads would have a pinkish skin colour.
Similar to eumelanin, the biosynthesis pathway of pheomelanin begins at tyrosine. It proceeds to the route with an end result of alanyl-hydroxy-benzothiazine in the presence of gluthathione or cysteine.
Word origin: Greek phaios ("dusky") + melas ("black, dark")