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If you're the lucky recipient of grey hairs, it might not just be that you're getting old, scientists have said that stress could in fact be to blame.
Experiments on mice have shown that stem cells that control skin and hair colour can become damaged after being under high stress levels, as published on nature.com.
The chance finding showed that mice that had dark fur turned completely white within a few weeks.
Researchers from America and Brazil said that exploring the findings more could lead to development of a drug that stops hair changing colour.
Although hair colour changing is mainly down to ageing and the natural process of getting old, the study shows that stress can be a factor in speeding it up.
Researchers from Sao Paulo and Harvard Universities said that the effects of stress were linked to certain cells that are responsible for producing melanin - the substance that causes hair and skin colour changes.
Professor Ya-Cieh Hsu, from Harvard, told the BBC: "We now know for sure that stress is responsible for this specific change to your skin and hair, and how it works."
The accidental findings were discovered when they noticed that, when doing another experiment, that pain in mice triggered adrenaline and cortisol to be released.
When their hearts were beating faster, their blood pressure rose, which affected their nervous system and caused acute stress.
This then caused the stem cells that produced melanin to be reduced.
Professor Hsu said: "I expected 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 any more - the damage is permanent."
Another experiment showed that the changes could be blocked by giving the mice a drug that treats high-blood pressure.
By comparing the genes of mice in pain with others, they realised that the protein causing damage when stressed is called cyclin-dependent kinase (CDK). When it was suppressed, the treatment stopped their fur from changing colour.
Professor Hsu added: "These findings are not a cure or treatment for grey hair. Our discovery, made in mice, is only the beginning of a long journey to finding an intervention for people.
"It also gives us an idea of how stress might affect many other parts of the body."
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