Experts have been pondering the question for years. Here’s what we know (so far).

Q: I went through a tough time two years ago, and my hair has since become much more gray. Could it be a result of the stress?

It’s natural to assume that stress contributes to gray hair. Just look at the various presidents who left office with many more silvery strands than when they went in. But if you dig into the research, you’ll find that few studies on the topic exist. And while some have found associations between premature graying and stress, no research has proved the link. “There’s still a lot we don’t know,” said Dr. Paradi Mirmirani, a dermatologist at the Kaiser Permanente Vallejo Medical Center in Northern California.

The Science of Stress and Gray Hair

In past studies, researchers have asked participants to fill out questionnaires about their hair color and stress levels, and then the scientists would see if they could link them.

In one study published in 2016, for instance, scientists surveyed more than 1,100 young Turkish adults and found that the 315 who reported prematurely graying hair had higher stress levels than those who didn’t. (Those with premature graying also had histories of alcohol use and chronic disease, and they had parents who went gray at a young age.)

But a mouse study published in 2020 took the research a step forward. In it, researchers stressed mice in various ways, including by injecting them with a chili-pepper-like chemical that induced a “fight-or-flight” response. This caused them to release the stress hormone norepinephrine, which, in turn, depleted their hair follicles of the stem cells involved with adding pigment to mouse fur. The hair then grew in gray.

The researchers demonstrated similar effects of high levels of norepinephrine on human stem cells in a lab as well, supporting the idea that the stress hormone is linked with graying in humans, said Ya-Chieh Hsu, a professor of stem cell and regenerative biology at Harvard University, and one of the authors of this research.

But studies on this topic are challenging to perform on people, because researchers can’t ethically induce artificially high stress responses in humans like they can in animals or cells, Dr. Hsu said.

One small human study published in 2021 still advanced the narrative: Researchers plucked various strands of hair from 14 volunteers who had at least some graying. Several of the strands were fully gray, some were partially gray and some hadn’t grayed at all. The scientists then created high-resolution digital images of the hairs and calculated when each strand went gray using estimates of how quickly hair grows.

They also asked the participants to plot out stressful experiences from the past year on a timeline, and rank them from least to most distressing. The researchers found that when a strand turned gray frequently corresponded with the most stressful moment of that volunteer’s previous year.

This was the first time a study linked specific stressful events with the exact moment hair began to gray, said Martin Picard, an associate professor of behavioral medicine at Columbia University and an author of the study.

It offered “our first real evidence that maybe stress does, in fact, play a role for some people,” said Dr. Victoria Barbosa, an associate professor of dermatology at the University of Chicago.

If such preliminary research continues to identify stress-related changes that cause hair graying, it may one day lead to treatments that can repigment hair, Dr. Mirmirani said. But we still need more and larger human studies to confirm the links, Dr. Barbosa said.

Future research might also help explain why stress is linked with hair graying in some people, but not in others, said Dr. Sindhuja Sominidi Damodaran, a dermatologist at the Mayo Clinic in Rochester, Minn.

It’s also too soon to know if easing stress could slow down or reverse premature graying.

Other Causes of Gray Hair

For most people, genetics is the main driver of hair graying, Dr. Barbosa said. If you have a parent who went gray at a young age, you’re likely to as well.

Certain medical conditions can cause hair to lose pigment prematurely, Dr. Barbosa said. Those include vitiligo, which causes patches of skin to lose color, and alopecia areata, a type of hair loss. An over- or underactive thyroid and chemotherapy treatments can also contribute to premature graying, Dr. Damodaran said. Deficiencies in iron, calcium and the vitamins B12 and D are correlated with going gray early too, she said; as are obesity and smoking.

Dr. Barbosa said that she likes to use graying as an opportunity to talk with her patients about accepting graying as a natural part of aging.

This can be especially liberating for women, she said, since “graying has always been socially more acceptable for men.”

Bron: New York Times / 13 Augustus 2024