The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acid, and their reduced forms.
Another common form of melanin is pheomelanin, a of benzothiazine units largely responsible for red hair and freckles. The increased production of melanin in human skin is called melanogenesis. It is stimulated by the DNA damages that are caused by UVB-radiation.Eumelanin is found in hair and skin, and colors hair grey, black, yellow, and brown.
In humans, it is more abundant in peoples with dark skin. But Pheomelanin becomes carcinogenic when exposed to Ultraviolet light” (Western Science Admission Excerpt)