Legend has it that Marie Antoinette’s hair turned gray overnight just before her beheading in 1791. Although the tale is untrue — hair that has already grown out of the follicle doesn’t change color — there is evidence that psychological stress is associated with graying hair in people. And a recent study conducted by researchers at Columbia University quantified the association and went one step further, proving that hair color can be restored when stress is eliminated.

“Understanding the mechanisms that allow ‘old’ gray hairs to return to their ‘young’ pigmented states could yield new clues about the malleability of human aging in general and how it is influenced by stress,” said the study’s senior author Martin Picard, associate professor of behavioral medicine at Columbia University Vagelos College of Physicians and Surgeons. “Our data adds to a growing body of evidence demonstrating that human aging is not a linear, fixed biological process but may, at least in part, be halted or temporarily reversed.”

Picard says that just as rings in a tree hold information about its past, our hair contains information about our biological history.

“When hairs are still under the skin as follicles, they are subject to the influence of stress hormones and other things happening in our mind and body. Once hairs grow out of the scalp, they harden and permanently crystallize these exposures into a stable form,” he says.

According to USA Today, a 2020 study conducted on mice found that under acute stress, hair in mice turns gray because of an overactive sympathetic nervous system. The “fight or flight” response can lead to a rapid depletion of melanocyte cells, the cells involved in creating pigment. And researchers have long noted that chronic stress can lead to various health and cognitive issues as well as loss of melanin, the dark brown or black pigment in the hair.

The Columbia study that was published in eLife found that gray hairs could naturally regain pigmentation across sex, ethnicities, ages, and body regions when stress levels were reduced. The researchers analyzed individual hairs from volunteers and then had study subjects record their stress levels in a diary. They noticed that a reversal of graying with the lifting of stress.

“There was one individual who went on vacation, and five hairs on that person’s head reverted back to dark during the vacation, synchronized in time,” said Picard. He added that while reducing stress in your life is a healthy goal, it may not necessarily turn your gray hair back to its normal color.

“Based on our mathematical modeling, we think hair needs to reach a threshold before it turns gray,” said Picard. “In middle age, when the hair is near that threshold because of biological age and other factors, stress will push it over the threshold, and it transitions to gray.

“But we don’t think that reducing stress in a 70-year-old who’s been gray for years will darken their hair or increasing stress in a 10-year-old will be enough to tip their hair over the gray threshold.”