Going grey can be distinguished
The grey hairs that develop with age really are signs of stress, at least of the cellular kind, say scientists.
Genotoxic stress, namely anything that damages the genetic code of life DNA, causes a malfunction of the cells ultimately responsible for hair colour.
The stress sets off a chain of reactions involving specialised cells called melanocyte stem cells, their work on mice in Cell journal reveals.
Similar mechanisms appear to be at work in humans too, they say.
The findings could help explain why people with Ataxia telangiectasia, a rare, neurodegenerative syndrome caused by a mutation in a gene called ATM, go grey prematurely.
In their study, Dr Emi Nishimura and colleagues found the ATM "caretaker" gene serves as a checks and measures system to stop melanocyte stem cells going awry.
It is the job of these cells within the hair follicles to make the mature pigment-producing melanocytes that give hair its youthful colour.
Researchers have already traced greying to the gradual dying off of the stem cells.
But this is not the only way the stem cells are depleted.
They also progressively make errors, turning or differentiating into fully committed pigment cells in the wrong place within the hair follicle, where they are useless for colouring hair.
And the latest work on mice shows irreparable DNA damage, as caused by ultraviolet light and ionising radiation, is responsible.
Dr Nishimura of Kanazawa University said: "Once stem cells are damaged irreversibly, the damaged stem cells need to be eliminated to maintain the quality of the stem cell pool.
"We found that excessive genotoxic stress triggers differentiation of melanocyte stem cells."
Dr David Fisher of Harvard Medical School, who has also studied the mechanisms of hair greying, said: "While it is unclear how this could be translated into a useful clinical practice currently, it does suggest that the loss of melanocyte stem cells during hair graying may be a protective process which removes potentially dangerous cells via a unique mechanism involving cellular differentiation."
Some scientists believe going grey is caused by a massive build up of hydrogen peroxide due to wear and tear of our hair follicles.
The hydrogen peroxide ends up blocking the normal production of melanin, an team of European scientists recently reported in the FASEB scientific journal, published by the Federation of the American Societies for Experimental Biology.