Graying of hair and stress have long been linked. However, until now, scientists were not able to explain the exact process by which this happens.
In new research published in the journal Nature, scientists at Harvard University have found evidence to back the age-old narratives that stress has a role in hair graying.
They reported that the activation of nerves, as part of the biological response triggered by stress, leads to irreversible cell damage in hair follicles.
“Everyone has an anecdote to share about how stress affects their body, particularly in their skin and hair – the only tissues we can see from the outside,” said Ya-Chieh Hsu, the senior author of the study and Harvard’s Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology. “We wanted to understand if this connection is true, and if so, how stress leads to changes in diverse tissues.”
Effects of Stress
There is hardly any part of the body that is immune to the impact of stress. Therefore, researchers in this study wanted to find out which specific body system impacted by stress leads to graying.
At first, the team of scientists posited that stress leads to an immune-mediated attack on pigment-producing cells. However, mice without immune cells continued to experience graying all the same.
Stress usually makes the amounts of the substance cortisol to rise in the body. So, the researchers also investigated this as a possible mechanism.
“But surprisingly, when we removed the adrenal gland from the mice so that they couldn’t produce cortisol-like hormones, their hair still turned gray under stress,” Hsu said.
Sympathetic Nervous System Activation
After considering other possible explanatory factors, the Harvard scientists observed that the sympathetic nervous system might hold the answer.
Hair follicles on the skin feature branches of sympathetic nerves, which are part of the mechanism driving the fight-or-flight response. Hsu and his colleagues observed that stress induces these nerves to release norepinephrine, which the surrounding pigment-producing stem cells take up.
The chemical released by sympathetic nerves promotes excessive activation of nearby stem cells. This causes the cells to hastily convert into pigment-producing cells.
Some stem cells are supposed to serve as a reservoir of pigment-regenerating cells to maintain hair color. The somewhat needless activation, however, results in a depletion of this reservoir and, hence, leads to graying.
These findings surprised the researchers.
“When we started studying this, I expected that stress was bad for the body – but the detrimental impact of stress that we discovered was beyond what I imagined,” said Hsu. “After just a few days, all of the pigment-regenerating stem cells were lost.”
Pigment production is no longer possible once the reservoir is depleted. Damage becomes permanent when this happens.
Foundation for Future Research
Scientists used a thorough approach in analyzing the harmful effects of stress in this study. Beginning with the whole-body response, they investigated down to the organ, cell, and molecular levels.
Findings made could prove helpful for having a better grasp of how stress impacts different tissues and organs in the body.
Before now, scientists knew little about how peripheral neurons regulate stem cells. This research has helped to make that clearer.
“With this study, we now know that neurons can control stem cells and their function, and can explain how they interact at the cellular and molecular level to link stress with hair graying,” said Isaac Chiu, an assistant immunology professor at Harvard Medical School.
By helping to understand the effects of stress on tissues and organs better, this study may aid future research to find ways to prevent unpleasant outcomes.