Chemical and biological aspects of melanin

This chapter discusses the chemical and biological aspects of melanin in condensed form. Melanin, the natural cosmetics of skin, hair, and feathers, represent broadly a group of natural and synthetic pigments of diverse origin and chemical functions. In nature, they usually occur in the form of insoluble fine granules accumulated in certain parts of animal and plant tissues. Some related synthetic melanins are also known. These are named after the compounds from which they were prepared via chemical and enzymatic oxidation, such as tyrosine-melanin, dopa-melanin, and catechol-melanin. The pigmentation of human skin has substantial protective, social, and cosmetic significance. Although melanins lack well-defined physical and spectral characteristics, they possess some effective chemical properties by acting as redox polymers, ion exchangers, and radical scavengers. The extensive studies of these chemical reactivities of melanin and putative melanin precursors have led researchers to infiltrate into many areas of scientific research, including the molecular biology of pigment-related genes