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Researchers find evidence that stress does turn your hair grey, and it can be reversed – you just need a holiday

But the hair dye market isn't about to implode, there are limits

Researchers have found that stress does indeed turn your hair grey, and that taking a break from all your worries sure would help a lot, even reversing the process – a discovery with potential ramifications for our understanding of the ageing process.

"Just as the rings in a tree trunk hold information about past decades in the life of a tree, our hair contains information about our biological history," senior author Martin Picard, PhD, explained of the team's research.

"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 crystallise these exposures into a stable form."

The team took a cohort of 14 individuals, seven men and seven women, and analysed their hairs using an off-the-shelf digital camera, microscope, and photo scanner, along with electron microscopy of hairs from two individuals. Once a hair pigmentation pattern (HPP) had been mapped, participants were then asked to complete a retrospective stress assessment – mapping stressful events to a timeline which can, in turn, be mapped onto the HPP.

"If you use your eyes to look at a hair, it will seem like it's the same colour throughout unless there is a major transition," Picard said. "Under a high-resolution scanner, you see small, subtle variations in colour, and that's what we're measuring."

The surprising part of the study wasn't the confirmation that stress can cause greying, but that removing the stress can reverse the effect.

"There was one individual who went on vacation," Picard said, "and five hairs on that person's head reverted back to dark during the vacation, synchronised in time. Our data add to a growing body of evidence demonstrating that human ageing is not a linear, fixed biological process but may, at least in part, be halted or even temporarily reversed."

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The finding flies in the face of a recent study in mice, which came to the same conclusion that greying can be caused by stress but found the mechanism was a loss of stem cells in the hair follicle – a process that could not be reversed, even if the stressor was removed.

"Our data show that greying is reversible in people, which implicates a different mechanism," said co-author Ralf Paus, PhD. "Mice have very different hair follicle biology, and this may be an instance where findings in mice don't translate well to people."

That's not to say the bottom is about to fall out of the hair dye market, though. "Based on our mathematical modelling, we think hair needs to reach a threshold before it turns grey," Picard warned. "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 grey.

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

The team's work is available here under open-access terms. ®

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