What causes skin black and white? Why some people are white, some people are black? Is it genetic factors or sun exposure? Let's hear how experts explain it!
Skin pigment can be divided into two categories: one is produced by the human body itself, which is called internal pigment, such as melanin, hemosiderin, bile pigment, etc.; the other is external pigment, which is called external pigment, such as carotene in food, foreign body (such as tattoo, coal dust and other sink disease), heavy metal (such as arsenic, gold and other sink disease), etc. The skin color discussed in this paper is mainly caused by the change of intrinsic pigment.
Melanin is the main pigment that affects skin color. Melanin is a kind of protein derivative, which is brown or black. Its formation and metabolism are jointly completed by melanocytes and keratin tissue of epidermis. Tyrosinase is the only known enzyme in melanin metabolism. The activation process of tyrosinase is closely related to biochemical process and physical environment in vivo. Therefore, the mechanism of melanin synthesis is quite complex. In addition to genetic factors, other clear and important aspects are as follows:
(1) DOPA is a catalyst of tyrosinase, which can accelerate the reaction.
(2) Sulfhydryl any factor that can reduce the sulfhydryl group in the epidermis, such as ultraviolet radiation, inflammation and so on, can promote the increase of melanogenesis.
(3) In the process of melanin metabolism, trace elements play the role of enzyme. If you lack trace elements, your hair will turn white.
(4) Under the action of sympathetic nerve, melanosomes concentrate in the center of melanocytes, and pigment decreases; on the contrary, parasympathetic nerve can increase pigment.
(5) Amino acids, vitamin pantothenic acid and folic acid may participate in the formation of melanin; vitamin C may make the pigment turn pale; vitamin A deficiency may cause excessive keratinization of hair follicle, reduce sulfhydryl group and cause pigmentation; niacin deficiency may cause pigmentation of skin sensitive to light.
(6) Endocrine factors such as melanin stimulating hormone secreted by the middle pituitary gland can promote the formation of melanin by increasing the level of copper ion in the blood, increasing the activity of tyrosinase; sexual hormone can increase skin pigment, especially estrogen can stimulate melanocytes to secrete melanin body, while progesterone can promote the transport and diffusion of melanin body, and the combined effect of estrogen and progesterone is more obvious.
In short, the black and white skin color mainly depends on the ability of melanocytes to produce melanin, not the amount of melanocytes.