| Abstract | Melanin is a family of macromolecular pigments found in humans, animals and plants. In humans, melanin is responsible for hair, eye and skin color but it is also present in the inner ear and the brain stem. In the skin, eye and hair, this pigment acts as a photoprotectant absorbing impinging UV radiation and dissipating it as heat. The protective action of melanin limits UV-induced DNA damage in skin as well as lipid oxidation and disulphide bond cleavage that affect the mechanical properties of hair. Two types of chemically distinct melanin are produced in mammals, the blackbrown eumelanin and the red-yellow pheomelanin. Eumelanin is formed by 5, 6-dihydroxyindole (DHI) and 5, 6-dihydroxyindole-2-carboxylic acid (DHICA) while pheomelanin is a polymer containing 1, 4-benzothiazine units. Pro-oxidative pheomelanin and anti-oxidant eumelanin are both present in hair and skin in macromolecular aggregates. Their different proportions result in a range of colors found in human hair. Color and other optical properties of melanin depend on its supramolecular architecture which has not been unambiguously established. Some researchers have proposed a path for mixed melanogenesis that results in a core-shell assembly of pheo and eumelanin while others have introduced a chemical disorder model. |
|---|
