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For
, people have believed that
turns hair grey. France's Queen Marie Antoinette's hair
turned white the
before she was beheaded during the French Revolution. More recently, the hair of presidents and other world
have quickly lost colour. The strains of
have gone to the roots of
, especially hair follicles. The researcher said the loss of the pigment-regenerating stem cells cannot be reversed. She said: "You can't regenerate
any more. The damage is
." She thinks stress could accelerate the aging
.