melanin

Melanin  is a ubiquitous natural pigment found in most organisms (spiders are one of the few groups in which it has not been detected). Human skin is repeatedly exposed to ultraviolet radiation (UVR) that influences the function and survival of many cell types and is regarded as the main causative factor in the induction of skin cancer, behaving like a sun umbrella for our cells. It has been traditionally believed that skin pigmentation is the most important photon-protective factor, since melanin, besides functioning as a broadband UV absorbent, aids in the acquiescence of vitamin D from sunlight. Sunlight exposure to the epidermis produces melanin in billions of individuals, causing a tan effect on the skin. Some believe that melanin somehow blocks vitamin D absorption; evidence about this is not clear. More opportunity for valid scientific study may be required. Many epidemiological studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin. For many dominant animals, melanin pigments are derivatives of the amino acid tyrosine. There are three basic types, namely eumelanin, pheomelanin, andneuromelanin. The most common biological type is eumelanin, which is a polymer, which in rudimentary form is a hydro-carbon. Pheomelanin is acysteine-containing red-brown polymer of benzothiazine units largely responsible for red hair and freckles. Neuromelanin is present in the brain, but its function remains obscure. The production of melanin in human skin is called melanogenesis. This occurs by means of a process called "ultrafastinternal conversion", which enables melanin to dissipate more than 99.9% of the absorbed UV radiation as heat (see photoprotection). This prevents the UVB radiation damage that is responsible for the formation of malignant melanoma and other skin cancers