London: The myth that stress can make one's hair gray or white has been around for a long time. Now, scientists have finally established it.
A new study by Kanazawa University in Japan has found that as pressure builds, the stem cells which replenish one's hair colour become damaged leaving the tell-tale silver crown, the 'Cell' journal reported.
According to the scientists, this is because stem cells in their hair follicles were forced to mature, slashing the production of melanin -- the chemical that gives colour to the hair and skin.
Interestingly, the very visible sign of ageing appears to also have a beneficial effect -- reducing cancer risk.
The scientists came to the conclusion after analyzing the effects of radiation and other chemicals on the fur of lab mice and then monitoring changes in the colour of their fur as well as the status of their stem cells.
By looking at the hair follicles under microscopes, they saw when the stem cells turned into other cell types and linked the change to greying hair. And a similar mechanism may operate in people, the scientists said.
"The findings challenge existing theories about how the body tries to protect itself when it suffers genetic damage from radiation or other toxins.
"People have speculated that cells die when their DNA is damaged by apoptosis, a scientific term for cell suicide. This would stop damaged cells from growing uncontrollably as tumours. But these findings suggest the body has another way to protect itself.
"Probably the tissue is trying to get rid of risky stem cell populations which have a lot of DNA damage," Dr Emi Nishimura, who led the study, said.
Added Dr David Fisher of Harvard Medical School: "Greying may actually be a safety mechanism. They've shown that this mechanism is actually removing damaged stem cells. The good news is if you do find yourself greying, you're probably better off not having those cells persist."
He said the findings suggested that early maturation and differentiation in other groups of stem cells could help prevent cancer as well.