Melanin: The Original Sunscreen

Melanin is crucial for sun protection and has an advantage for skin of colour (SOC) in preventing photocarcinogenesis. Human migration to different geographies played a role in cutaneous pigmentation, contributing to the difference in skin colour across races and ethnicities. The two melanin moieties, pheomelanin and eumelanin and their relative distribution in human skin, significantly influence the level of the photoprotection, while across races, the number of melanocytes in a given anatomical location remains similar. Melanin production is controlled by a large number of genes, but MITF is the main coordinator of melanocyte behaviour. Eumelanin is photoprotective and its presence reduces the induction of procarcinogenic stimulus, while a lack of eumelanin or the presence of pheomelanin increases oxidative activity in the cell. Skin of colour appears to have inherent advantages against photodamage and photocarcinogenesis, owing to the ability of melanin to provide broad-spectrum protection against solar light. The distribution and transfer of melanosomes within the cells in the human epidermis, as well as the specific response towards differentiation over proliferation, provides higher levels of photoprotection in dark-skinned individuals compared to the lighter skin types. In addition, enhanced repair mechanisms after sun exposure provide further protection against cutaneous carcinogenesis, in the former group. Overall, the skin can be said to have evolved to be a specialized sunscreen, rather than just a physical sunblock.