If for some time to be in the sun, the human skin inevitably becomes darker - tans and hair, on the contrary, become more light - fade.
This phenomenon seems to be a simple and familiar, but at the level of physiological reasons are not so obvious as it might seem at first glance.
Why the skin becomes darker in the sun
Among other cells in the skin contains specialcells in the form of stars - melanocytes, whose main task - to develop a special pigment - melanin. Last responsible for skin color: the melanin is more, the skin darker. However, if the skin of any color are constantly exposed to solar radiation, it will inevitably become even darker.
Familiar tan - not that other, as a well-organized defensive process: it prevents penetration into the deeper layers of skin UV excess.
How is this process? Sunlight on the prominent eyes a center frequency comprises including ultraviolet rays (UV). It is due to ultraviolet light skin and darker. At the cellular level is more active than usual, the development of pigmenting the skin while protecting it from ultraviolet rays melanin. And if your skin every day subjected to irradiation by sunlight, it will inevitably become increasingly more dark shade.
Why does the sun lighten your hair become
With hair causes and effects lookquite differently. The main construction material of hair - keratin protein substance from which also consist fingernails and animals - and even horns. Hair does not refer to living tissues, but they grow out of a living body - skin and hair color depends on the amount of melanin produced by the melanocytes of the skin that the hair roots. Sami hair pigment melanin thus not able to produce.
Produce melanin skin has a protectivefunction - absorbs excessive exposure to ultraviolet rays. However, the hair unable to produce melanin, so the sunlight over time lose their original pigmentation.
Aggressive UV rays, acting onhair for a long time, making them lighter, that is, to develop skin melanin gradually destroyed, and produce a new hair color themselves no longer able to. That is why, if a long time to be highly active under the summer sun or the sun of tropical and equatorial latitudes, even the darkest hair are at least a bit lighter.
Thus, the increased production of melanin in order to protect it from the sun causes skin darkening. And the destruction of the melanin in the hair under their exposure to the sun causes a slight clarification.