Why some People's Skin go Black?
It is our long-life experience that when we remain directly exposed to the sunshine most of the time, our skin turns black. Why this happens? Everyone has its own feelings about this blackening of skin. Most of the people, being over-conscious to their beauty rather than health, complain that this blackening affects their beauty. So they feel that turning black is not a good thing in nature. If we come to know the real theory behind actual processes involved in blackening of skin, we will get surprised.
Nature has designed the human body in a super-perfect way. Our body has certain mechanisms that protect us from ever-changing outer environment. Coming to the point with a little bit scientific details, we will come to know that this blackening of skin is actually protecting us. The upper layer of our skin contains two type of cells; keratinocytes and melanocytes. Don't worry to memorize these names, as the point is to just have an understanding of scientific explanation. The melanocytes produce a certain type of pigmented-protein called melanin which has the capability to absorb harmful radiations exposed to skin. This melanin protein is transported to keratinocytes to cap over their nucleus. This capping of melanin layer protects the keratinocytes from the harmful solar radiations.
The very upper superficial layer of our skin is being replaced every two to three weeks. A regular melanin production is needed to protect this ever-replacing layer. When we are exposed to the sunlight containing harmful ultraviolet radiations, the cells in upper layer of skin get their DNA damaged or altered. This alteration or damage activates the protection mechanism of our body. A stimulus is sent to the brain that something is causing damage to the skin cells. Now the brain initiates a hormonal mechanism to overcome this problem. A certain hormone, melanocyte-stimulating hormone (MSH), is produced and it acts on melanocytes to increase their activity to produce melanin. There will be no increase in number of melanocyte cells, but their size and efficiency to produce melanin is increased. This caps the nucleus of cells in upper layer of skin, turning you black and resultantly protecting you from effects of harmful radiations such as sunburn, skin cancer etc.
Have you ever thought why the people living near equator, or where the sunshine is highest, are darker? On the other hand the people living in cloudy areas, or where sunlight exposure is low, are white in skin color. The answer lies in the mechanism described above. When you are living in the environment where sunlight intensity and exposure is higher, you should have black skin to protect yourself against harmful ultraviolet radiations. On the other hand, if you are in cold, cloudy or humid area, most of the harmful radiations in the sunlight are absorbed by clouds or water molecules. So there is no specific need of black skin. So your genetic code is designed by the nature as per your territory to make your life better in that area.
Some patients with other diseases like Cushing's syndrome, Addison's syndrome or even simple fever also complaint about blackening of their skin. Further, when we get injured, we feel that the injury site being repaired is also blackened. Even this is observed in normal healthful conditions of a pregnant woman, though this blackening is on specific sites such as armpit, legs etc. Specifically a vertical black line below navel and a black circle around breast nipples are most common in pregnancy. Now the theory behind this blackening is that melanin is not only produced by melanocytes in the skin, but also is a byproduct of various other hormones. So if you have some hormonal disorder, you may be a victim of blackened skin. To the same reason, blackening in a pregnant woman is due to various hormonal changes occurring during pregnancy. A lucky woman can get this blackening reversed after some weeks after delivery or childbirth. Others may also have it permanently.
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