Why Does Stress Turn Our Hair Gray? Harvard Researchers Unlock Answers

CAMBRIDGE, Mass. — It’s not exactly breaking news that stress can cause one’s hair to turn gray, but up until now, there hasn’t been a conclusive scientific explanation as to why. Now, researchers at Harvard University believe they’ve figured out the biological machinations that lead to stress-related hair graying.

Feelings of stress activate nerves associated with our fight-or-flight response. These activated nerves then cause permanent damage to the pigment regenerating stem cells in our hair follicles, researchers say. These findings are yet another chapter in the seemingly never-ending compendium of how stress can adversely influence our bodies.

“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,” says senior author Ya-Chieh Hsu, the Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology at Harvard, in a release. “We wanted to understand if this connection is true, and if so, how stress leads to changes in diverse tissues. Hair pigmentation is such an accessible and tractable system to start with — and besides, we were genuinely curious to see if stress indeed leads to hair graying.”

Stress is known to affect the entire body, so the research team were first tasked with establishing which bodily system was connecting stress to hair color. Initially, they theorized that stress may induce an immune attack on pigment-producing cells, but that hypothesis was disproven when a group of lab mice lacking any immune cells still showed gray hair development. They also considered the possibility that the hormone cortisol may be involved, but again, that idea proved to be incorrect.

So, through a simple process of elimination, the study’s authors settled on the sympathetic nerve system and its control over the fight-or-flight response. Each hair follicle on our skin contains sympathetic nerves. Stress causes these nerves within our hair to release a chemical called norepinephrine, which is then absorbed by close-by pigment-regenerating stem cells.

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Stem cells in our hair follicles essentially act as a backup supply of color-producing cells for our hair. When our hair grows or regenerates, these stem cells help supply our natural hair color. However, in the event of stress and the release of norepinephrine, our stem cells over-activate, prematurely depleting our hair’s color reserves.

“When we started to study this, I expected that stress was bad for the body — but the detrimental impact of stress that we discovered was beyond what I imagined,” Hsu explains. “After just a few days, all of the pigment-regenerating stem cells were lost. Once they’re gone, you can’t regenerate pigment anymore. The damage is permanent.”

“Acute stress, particularly the fight-or-flight response, has been traditionally viewed to be beneficial for an animal’s survival. But in this case, acute stress causes permanent depletion of stem cells,” adds lead study author Bing Zhang, a postdoctoral fellow.

Besides just answering a long lingering question regarding stress and gray hair, this study can also provide some new insight into the overall effect of stress on various organs and tissues in the human body.

“Understanding how our tissues change under stress is the first critical step towards eventual treatment that can halt or revert the detrimental impact of stress. We still have a lot to learn in this area,” Hsu concludes.

The study is published in Nature.

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