Melanin

Melanin (/ˈmɛlənɪn/ ^ⓘ; from Ancient Greek μέλας (mélas) 'black, dark') consist of oligomers or polymers arranged in a disordered manner which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. They have been described as "among the last remaining biological frontiers with the unknown".

There are five basic types of melanin: eumelanin, pheomelanin, neuromelanin, allomelanin and pyomelanin. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino acid tyrosine is followed by polymerization. Eumelanin is the most common type. Pheomelanin, which is produced when melanocytes are malfunctioning due to derivation of the gene to its recessive format, is a cysteine-derivative that contains polybenzothiazine portions that are largely responsible for the red or yellow tint given to some skin or hair colors. Neuromelanin is found in the brain. Research has been undertaken to investigate its efficacy in treating neurodegenerative disorders such as Parkinson's. Allomelanin and pyomelanin are two types of nitrogen-free melanin.

In the human skin, melanogenesis is initiated by exposure to UV radiation, causing the skin to darken. Eumelanin is an effective absorbent of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, eumelanin is thought to protect skin cells from UVA and UVB radiation damage, reducing the risk of folate depletion and dermal degradation. Exposure to UV radiation is associated with increased risk of malignant melanoma, a cancer of melanocytes (melanin cells). Studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin, i.e. darker skin tone.