The sympathetic nervous system, which prepares the body to respond to threats, also plays an important role in the whitening process, according to a study published in the journal Environment in Nature. “Under normal circumstances, the sympathetic nervous system is a kind of emergency system that provides the fight-or-flight response,” says Ya-Chie Xu, a stem cell biologist at Harvard University. In fact, it should be extremely beneficial, or at least the effect should be temporary and reversible.”
The sympathetic nervous system activates many biological responses, such as increased blood flow to the muscles and increased mental focus. However, according to the results of the study, the same nervous system in some cases irreversibly damages the stem cells of the hair follicles. Dr. Xu said the findings are the first scientific evidence of a link between stress and graying hair. Since stress affects the entire body, it is important to determine which physiological system transmits the effects of stress to the hair follicles. As part of the study, the scientists first hypothesized that stress causes the immune system to attack melanocyte stem cells. They subjected mice to acute stress with the irritant chemical capsaicin found in capsicum. But they found that even mice without immune cells showed graying of their hair.
The next step was to study the effect of the stress hormone cortisol. Even mice that have had their adrenal glands removed to prevent cortisol production have been shown to experience gray hair when under stress. It seems that the system responsible for the formation of gray hair strands is the sympathetic nervous system, which extends to every hair follicle in the skin. The sympathetic nervous system releases the neurotransmitter norepinephrine, which is retained by nearby melanocyte stem cells. After that, melanocyte stem cells begin to multiply and turn into pigment-producing cells. These cells, on the contrary, leave their places in the root of the follicle and destroy the source of hair pigmentation.
In the aforementioned study, acute stress completely depleted the mouse melanocyte stem cell population in just five days. In experiments carried out in Petri dishes, it turned out that norepinephrine stimulates the reproduction of human melanocyte stem cells in the same way; therefore, the sudden acceleration of the hair whitening process affects people in a similar way.
“I was stunned by how dramatic the changes were,” said Mayumi Ito, a biologist at New York University. “A decrease in the number of melanocyte stem cells initially leads to the formation of gray hair, which eventually turns into gray or white fur – just like aging accelerates the formation of gray hair in humans…”
Dr. Xu and his team also found that the whitening process in mice can be stopped with drugs known as CDK inhibitors; This group of drugs inhibits the reproduction of stem cells or blocks the release of norepinephrine. The findings highlight the consequences of triggering a survival mechanism in the absence of a life-threatening situation. Biologist Subroto Chatterjee of Johns Hopkins University said: “Stress is a normal part of life; however, there are situations where stress can be helpful, as well as situations where it can be harmful. Stress is just one of the factors influencing the rate of hair graying, and genetics and diet also have a huge impact.”
Dr. According to a 2018 study by Chatterjee and his team, a high-fat, high-cholesterol diet in rats not only causes inflammation of the arteries, but also causes graying and hair loss.
Dr. Xu and his team’s new study is an important step towards understanding the effects of stress on different tissue types. Dr. Xu said, “If we can understand how tissues and stem cells change under stress, we may eventually be able to create treatments that can stop or reverse these damaging effects.”