For centuries, people have said stress causes hair to go gray, and Harvard researchers in a study published Wednesday in Nature found evidence to back up the age-old claim.

Infographic: How to be a less-stressed leader

Can stress change our hair color?

"Everyone has an anecdote to share about how [stress] affects their body, particularly in their skin and hair," according to Ya-Chieh Hsu, senior author of the study and an associate professor of stem cell and regenerative biology at Harvard University.

For instance, some people point to former President Barack Obama, whose hair went from dark to gray during his presidency, and it was said that Marie Antoinette's hair turned white overnight as she waited to be executed by guillotine.

But while it's popular to believe that stress can actually turn people's hair gray, there's been limited research on the subject to validate the theory. 

Yes, stress can make you go gray

A group of Harvard researchers set out to get to the bottom of the issue. "We wanted to understand if this connection is true, and if so, how stress leads to changes in diverse tissues," Hsu said.

Since stress impacts the entire body, the researchers developed various hypotheses regarding how stress affects various systems in the body to change hair pigment. To test the hypotheses, they exposed mice to stress hormones and recorded the effects.

The team first hypothesized that stress could cause an immune attack on cells that produce pigment, but that turned out to be a dead end. When they exposed the mice to acute stress, the hair of all of the mice turned gray— even the mice that had no immune cells.

Next, the researchers studied whether the stress hormone cortisol played a role in graying. "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," according to Hsu.

Finally, the researchers turned to the sympathetic nervous system, which promotes blood flow to muscles, increases mental focus, triggers our fight or flight response, and, as it turns out, plays a role in the graying process.

For years, researchers have known that pigment-making stem cells called melanocytes give hair its color and that losing those cells can rid hair of its natural hues. But why people lose those cells has been a mystery until this latest study.

It turns out, the sympathetic nerve system which branches out to each hair follicle, is the driving factor. When stress levels rise, the sympathetic nervous system triggers a chemical called noradrenaline that overly stimulates the stem cells causing them to become damaged and deplete over time. Without those stem cells the hair strands become more transparent or gray, the researchers said.

Hsu said, "Normally, the sympathetic nervous system is an emergency system for fight or flight, and it is supposed to be very beneficial or, at the very least, its effects are supposed to be transient and reversible." However, according to Hsu, "After just a few days, all of the pigment-regenerating stem cells were lost. Once they're gone, you can't regenerate pigments anymore. The damage is permanent."

Discussion

The study is the first to find a relationship between stress and hair graying, according to Hsu.

Hsu said, "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."

But Subroto Chatterjee, a biologist at Johns Hopkins University who was not involved in the study, said that the findings indicate the downside to triggering stress unnecessarily. "[T]here are situations where stress is helpful and situations where it is detrimental," Chatterjee said.  

According to Hsu, the findings also could help researchers understand how stress can impact other organs and tissues.

"By understanding precisely how stress affects stem cells that regenerate pigment, we've laid the groundwork for understanding how stress affects other tissues and organs in the body," Hsu said. "Understanding how our tissues change under stress is the first critical step toward eventual treatment that can halt or revert the detrimental impact of stress. We still have a lot to learn in this area" (Lau, Harvard Gazette, 1/22; Sheikh, New York Times, 1/22; Walter, Discover, 1/22; Sample, The Guardian, 1/22).