The skin generally turns brown by exposing it to UV light. Of course and also used by most people, this is the light of the sun. With the sun bath humans can cover also a part of their Vitamin D (Cholecalciferol) need with the help of the UVB light.
Vitamin D is essential for the human body. It belongs to the fat-soluble vitamins and can be produced by the body with the help of UVB radiation in the skin from the precursor of the vitamin, 7-dehydrocholesterol. Vitamin D is important for the calcium balance in bones and blood.
The tanning itself is also largely caused by UVB radiation. UVB radiation belongs to the superordinate term of ultraviolet radiation, which also includes the longer-wave UVA radiation. Ultraviolet radiation is invisible to the human eye and has a longer wavelength than X-rays, which are also very well known, but the wavelength is still shorter overall than that of light that is visible to humans.
Melanocytes
The fact that the skin turns brown is mainly due to melanocytes, which are found in the uppermost layer of the skin. The melanocytes produce melanin, which is a black-brown or reddish dye responsible for the coloring of the skin. However, it not only colors the skin, but also the choroid in the eye and the hair of humans.
Melanin is released to protect the skin from UV radiation. The more sunlight reaches the skin, the more melanin is released and the more tanned the skin becomes. In addition to melanin, the thickening of the horny layer protects us from the dangerous radiation.
Excessive radiation is therefore dangerous because it can change our DNA in our cells, which in turn can lead to errors in cell division. If the body cannot correct the mistakes, or if too many mistakes happen, cells can grow uncontrolled and a tumor can develop. In general, the skin should only be exposed to the sun to a small extent. But if you take certain precautions, you can get a nice tan even without sunburn.
