Natural peroxide bleach is responsible for hair turning gray or white with age, scientists have discovered.
The same substance responsible for Marilyn Monroe's golden locks also gives Alistair Darling his distinctive white thatch.
Researchers found hydrogen peroxide created by cells plays a role in age-related loss of hair color.
Professor Heinz Decker, of the Institute of Biophysics at Mainz University in Germany, said: "With advancing age, hydrogen peroxide builds up in larger amounts in the hair follicle and ultimately inhibits the synthesis of the color pigment melanin."
Hydrogen peroxide, or H2O2, is a byproduct of metabolism, the process by which cells burn fuel for energy.
Generated in small amounts throughout the body, the chemical is normally neutralised by an enzyme which breaks it down into water and oxygen. With age, levels of the enzyme fall and hydrogen peroxide builds up.
Working with colleagues from Bradford University, Professor Decker found hydrogen peroxide interfered with melanin production by disrupting a biological pathway.
At the same time it inhibited enzymes needed for repair of damaged proteins. This set off a cascade of events leading to the gradual loss of pigment from the hair's root to its tip.
