It turns out that stressful nerve impulses cause depletion of the resources of stem cells involved in the formation of pigment hair structures.
It is known that with severe fright or nervous shock, hair can quickly turn gray. But how is this possible and why is it happening?
Often, people who are often nervous and worried turn gray faster than others. But it is not always clear where to look for the underlying cause of early graying - stress, age-related changes, diseases or hereditary predisposition.
Through a series of studies, scientists from Harvard University have proven that stress alone is enough for early graying. The shade of the hair depends on the number of melanocyte cells in which the pigment substance melanin accumulates. Melanocytes themselves are formed from certain stem cells that are localized directly in the hair follicle. In young people, they are periodically renewed, but over the years their number decreases, and the hair gradually becomes gray.
Through experiments with rodents, scientists have discovered that regular stimuli such as pain, infringement of something, difficult psychological situations lead to a decrease in the number of stem cells in the follicle and, as a result, to the appearance of gray hair.
Initially, it was assumed that the hair follicle is exposed to a stress hormone - corticosterone. There was another theory: the body's immune defense under the influence of stress mistakenly attacks the corresponding stem cells. However, it turned out that there is another main reason. The fact is that melanocyte stem cells have endings that are sensitive to norepinephrine, which is involved in the stress mechanism. Thus, it helps to create nerve circuits that "decide" what will be the reaction to stress. When such receptors were “turned off” in rodents, stress graying of hair ceased.
But what is the purpose of stress gray hair? Experts explain that for many animals - for example, monkeys - gray hair is a sign of vitality, experience and strength. This means that, for example, a gray-haired male is always more respected and can even lead a flock. However, this is just speculation, and it is likely that gray hair does not carry any evolutionary burden.
Presumably, melanocyte stem cells are not the only structures that respond to stress. Similar processes are observed with blood stem cells: as a result of the "shake-up" they leave their zones in the bone marrow and stop renewing. It is possible that frequent or deep stresses negatively affect other types of stem cells. This could explain a lot - for example, why the immune defense is weakened against the background of stress, and age-related changes occur faster.
Information is presented on the pages of the publication Nature