Scientists uncover key cause of grey hair

For years, people have believed that stress causes grey hair, but scientists were not sure exactly how this happened. Now, researchers from Harvard University have found the key reason behind this connection.

Their study, led by Ya-Chieh Hsu and published in Nature, reveals that stress damages pigment-regenerating stem cells in hair follicles, leading to permanent hair color loss.

The Search for Answers

The study started with a simple question: Does stress really cause grey hair, and if so, how? Since stress affects the entire body, the researchers needed to identify which system was responsible for this change in hair color.

At first, they thought stress might trigger an immune response that attacked pigment-producing cells. However, when they tested mice that lacked immune cells, they still developed grey hair under stress. This meant that the immune system was not the cause.

The team then examined other possibilities and found the answer in the sympathetic nervous system—the part of the body that controls the fight-or-flight response. This system helps the body react to danger, but the researchers discovered that it also plays a surprising role in hair color.

How Stress Turns Hair Grey

The sympathetic nervous system has nerves that reach into every hair follicle. When a person experiences stress, these nerves release a chemical called norepinephrine. This chemical is usually helpful because it prepares the body to respond to threats, but in hair follicles, it has an unexpected effect.

Hair color comes from pigment-producing cells, which are created by special stem cells in the hair follicle. These stem cells act as a backup supply, turning into pigment-producing cells when needed. Under normal conditions, this reserve of stem cells is gradually used over time.

However, under stress, the release of norepinephrine causes the stem cells to become overactive. Instead of slowly turning into pigment-producing cells as needed, they all convert at once. This quickly depletes the reserve of stem cells, leaving none behind to produce pigment in the future. Once this happens, hair loses its color and turns grey permanently.

A Survival Response With Unintended Consequences

The fight-or-flight system is designed to help the body react to danger by increasing alertness and energy. But in the case of hair follicles, its activation has an unwanted side effect—permanently removing pigment-producing stem cells. This suggests that stress can cause lasting damage to certain cells in the body, not just temporarily affect them.

What This Means for Health

While grey hair itself is harmless, this study shows that stress can have deeper effects on the body at a cellular level. The researchers believe that similar processes may be happening in other organs, where stress could be damaging important cells over time.

By understanding how stress affects the body, scientists may be able to find ways to prevent or reduce these harmful effects. Future research could lead to treatments that protect stem cells and other critical cells from stress-related damage.

This study provides important insights not only into why stress turns hair grey but also into the broader impact of stress on overall health. Managing stress could be more important than we think—not just for maintaining hair color, but for protecting the body from long-term damage.