A team of scientists from Harvard has discovered a new mechanism in the life of the hairline of the human skin. They looked for the reasons for the formation of "goose bumps" or characteristic creeps on the body, and eventually came to stem cells. And they found that there is a direct connection between this reflex action and the deep control system of hair regeneration.
When it gets cold outside, the sympathetic nerves send a signal to a small bundle of muscles that connects the hair follicle to the skin. The muscles contract, the follicle shifts, a characteristic swelling forms on the skin, and the hair protruding from it rises above the skin. There is no practical effect, because human hair has long been too sparse for bulging hair to form a thermal protection. It works in animals with thick fur, but not in humans.
But why, in the course of evolution, did we lose body hair, but did not get rid of this vestige? Probably the reason is that goose bumps are only part of the reaction, its fast phase. The same sympathetic nerve, when viewed under an electron microscope, appeared to be associated with stem cells in the hair follicle. And in fact, its triggering is necessary in order to start the process of hair regeneration, stimulate their rapid growth and increase in volume.
Scientists have come to the conclusion that this mechanism is two-stage, and one sympathetic nerve activates both stages. Goosebumps are an informational message, a message to the body that it has become dangerously cold and that measures need to be taken. But it is too risky to rely only on them, therefore, immediately, in parallel, a signal is sent to the hair follicle with an indication to start the regeneration process. So that the body, in response to the cold, begins to grow a thick protective cover using stem cells. But this ability has long been lost by man, so for us everything is limited to goose bumps.