A person turns gray because the pigment melanin, which dyes the hair, ceases to be produced. It is produced by special cells - melanocytes. They sit at the base of the hair. Then melanin is transferred to the cells of the growing hair - keratinocytes. And it stops being produced for several interrelated reasons. In melanocytes, with age, enzymes that decompose hydrogen peroxide H2O2 begin to work worse (why is not known for sure). Accumulating in large quantities, hydrogen peroxide damages the enzyme tyrosinase, which is responsible for the synthesis of melanin. In addition, other proteins are damaged. For example, proteins responsible for the transfer of melanin from melanocytes to keratinocytes stop working. The very important protein Bcl2, which protects melanocytes from apoptosis, or programmed death, also stops working. Gradually, melanocytes die, and stem cells,from which they are formed, divide with age more and more slowly and do not make up for their loss.
When melanin is no longer produced, the hair turns white. Its structure is changing in parallel. Interestingly, graying hair cells often divide faster - especially in the core. The hair grows faster, its core becomes less dense, voids, air bubbles form in it. Light "bumps" into these voids, scatters in different directions, and because of this, the hair appears white (for the same reason, the foam, consisting of transparent water, appears white).
Although the amount of hydrogen peroxide can increase under stress, it cannot spread along the entire length of the hair and discolor them - after all, living cells where it is formed are only at the base of the hair. Therefore, you cannot turn gray in 5 minutes. And yet, cases of rapid "graying" have been documented by scientists and doctors. How does it happen?
It turns out that you can quickly turn gray due to a special form of baldness, often associated with severe stress - diffuse hair loss. Sometimes, mainly colored hair falls out, but gray remains (why is unknown). A case of this rare form of baldness and without any prior stress has been described. There are also known cases when, after diffuse baldness, hair of normal density again grew. In one case, they were completely gray, and in the other, they were painted. But in all scientifically described cases that I managed to find, a person sat down not in 5 minutes, but in several days or weeks.
Sergey Glagolev, Vera Bashmakova
