Stress can turn your hair gray and you can blame it on body's fight-or-flight response, say scientists
When Marie Antoinette was captured during the French Revolution, her hair reportedly turned white overnight. In more recent history, John McCain experienced severe injuries as a prisoner of war during the Vietnam War —) and lost color in his hair.
There have been a lot of anecdotes connecting stressful experiences with the phenomenon of graying hair. Now, scientists from Harvard University have discovered exactly how the process plays out. Stress activates nerves that are part of the fight-or-flight response, which, in turn, causes permanent damage to pigment-regenerating stem cells in hair follicles, the team explains. The researchers, however, add that stress is not the only reason hair can turn gray.
According to senior author Ya-Chieh Hsu, the Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology at Harvard, this study is the first to establish that there is a real biological connection between stress and hair turning gray, and the first to discover exactly how it happens.
"In this study, we used mice to look at how stress affects the specific stem cells in hair follicles that are responsible for making pigment cells. We confirmed that stress does indeed cause hair to lose its color, but more importantly, we also figured out how this happens. This research is critical in helping scientists understand how stress affects the body. We now know for sure that stress is responsible for this specific change to your skin and hair, and how it works. These findings are not a cure or treatment for gray hair. Our discovery is only the beginning of a long journey to finding an intervention for people," Hsu tells MEA WorldWide (MEAWW).
The researchers say by understanding precisely how stress affects stem cells that regenerate pigment, they have laid the groundwork for understanding how stress affects other tissues and organs in the body.
According to Hsu, it is the first step towards developing ways to block the damaging effects of stress in the future. "It has been so exciting to discover this important mechanism, which will point us and other researchers in the right direction. In the future, we do hope to develop a therapeutic that is both effective and safe, but that will not be for a few years," Hsu tells MEAWW.
The finding, published in Nature, underscores the negative side effects of an otherwise protective evolutionary response, says the team.
"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," says Harvard postdoctoral fellow Bing Zhang, the lead author of the study, in the analysis.
Because stress affects the whole body, researchers first had to narrow down which body system was responsible for connecting stress to hair color.
"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. 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," says Hsu.
The team initially hypothesized that stress causes an immune attack on pigment-producing cells. However, when mice lacking immune cells still showed hair graying, researchers turned to the hormone cortisol. But once more, it was a dead end.
"Stress always elevates levels of the hormone cortisol in the body, so we thought that cortisol might play a role. 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," says Hsu.
After eliminating different possibilities, researchers honed in on the sympathetic nerve system, which is responsible for the body's fight-or-flight response.
Sympathetic nerves branch out into each hair follicle on the skin. The researchers found that stress causes these nerves to release the chemical norepinephrine, which gets taken up by nearby pigment-regenerating stem cells.
In the hair follicle, certain stem cells act as a reservoir of pigment-producing cells. When hair regenerates, some of the stem cells convert into pigment-producing cells that color the hair.
Researchers found that the stress hormone norepinephrine from sympathetic nerves causes the stem cells to activate excessively. The stem cells all convert into pigment-producing cells, prematurely depleting the reservoir.
“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. 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," says Hsu.