Melano... what?

Melanocytes are cells present in the bottom layer of the skin's epidermis, the middle layer of the eye, the inner ear, meninges, bones and heart. Through a process called melanogenesis, these cells produce melanin, the pigment that gives hair, skin, and eyes the color they have. So next time you sun bath and become tanned, instead of burned you can say your melanocytes did a quite well melanogenesis job! Ok, don't be so nerd!

Position of melanocytes in the skin

Produced from the amino acid tyrosine, two forms of melanin exist in hair and skin: the most common called eumelanin, a brown-black polymer, and pheomelanin, a red-brown polymer, largely responsible for red hair and freckles.

Melanocytes comprise from 5% to 10% of the cells in epidermis. So the difference in skin color between light- and dark skinned people is due not to the number (quantity) of melanocytes in their skin, but to the melanocytes' level of activity (quantity and relative amounts of eumelanin and pheomelanin). Skin color is formed as follows: melanocytes insert granules of melanin into specialized cellular vesicles which is then transferred into the other skin cells of the human epidermis. The melanosomes in each recipient cell accumulate "over" the cell nucleus protecting the DNA from mutations caused by radiation of the sun's ultraviolet rays.

People whose ancestors lived for long periods in the regions of the globe near the equator generally have larger quantities of eumelanin in their skins. This makes their skins brown or black and protects them against high levels of exposure to the sun, which more frequently results in melanomas in lighter skinned people. On the other hand, albinos produce fewer or have a lack of the enzyme that is required for melanocytes to produce melanin from tyrosine!

Map of skin color distribution!

Why some get more and others get less suntanned? Because there are both basic and activated levels of melanogenesis and lighter-skinned people generally have low to basic levels of melanogenesis.

The most recent scientific evidence indicates that all humans evolved in Africa followed by migration, populating the rest of the world. It is most likely that the first people had relatively large numbers of eumelanin producing melanocytes and, accordingly, darker skin (as displayed by the indigenous people of Africa, today). As some of these original peoples migrated and settled in areas of Asia and Europe, the necessity for eumelanin production decreased in climates where radiation from the sun was less intense. Thus variations in genes ("sequences of DNA responsible for a characteristic in our body") involved in melanin production began to appear in the population, resulting in lighter hair and skin in humans residing at northern latitudes.

Light-skinned peoples who migrated toward the equator had to acclimatize to the much stronger solar radiation. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. This is the physiological purpose of sun tanning. Dark-skinned people, who produce more skin-protecting eumelanin, have a greater protection against sunburn and the development of melanoma, a potentially deadly form of skin cancer.

This doesn't mean that we can go around exposing ourselves to the sun without thinking before.

Check the next post to know what to do! Take care!


Sourcesssss: Wikipedia, NAtional Cancer institute, SEER