Why do people get tanned? Will black people get a tan?

There are two reasons why people are easily tanned by the sun. One is due to the ultraviolet radiation from the sun. On the other hand, human aging cells also contain melanin. But when people are young, their metabolism is vigorous, and the speed of cell regeneration far exceeds the speed of cell aging. Newborn cells have the function of decomposing melanin. When there are enough new cells, they can break down all the melanin in the body. With the increase of people's youth, the metabolic level gradually declines, and the ability to decompose melanin becomes weaker and weaker, as does middle age.

When the skin is exposed to thermal radiation or sunlight, melanocytes located in the basal layer are stimulated and activated. They exist in basal cells at the ratio of 10: 1. These cells are dendritic and shuttle between epidermal cells. Melanocytes contain pigment particles, and melanosome is synthesized in rough endoplasmic reticulum, which will catalyze tyrosine tandem reaction to produce melanin protein. At the same time, tyrosinase will lose its activity and serve as a transporter to transfer it to keratinocytes. The more melanin protein is transferred to keratinocytes, the darker the skin color. After people with the same skin color are exposed to the sun for the same time, why are some people tanned and some people's skin has not changed much? This is related to many factors. Mainly depends on how much melanin is produced and how much melanin is transferred to keratinocytes, that is, the more melanin is produced and transferred to keratinocytes, the darker the skin color, and vice versa.

There is no doubt that black skin is black, which is determined by genes and inherited. Black skin is black because there are many melanin. The reason why there is more melanin is that black ancestors are generally distributed in tropical areas, close to the equator, where the weather is hot and the sun is high, so the ultraviolet level is high. Among the ancestors of black people, people with more melanin are easy to survive, while people with white hair are in that environment. It can't resist ultraviolet rays, so it is more likely to die. In this case, generation after generation, people who are always black can live better, so today, they are all black! .