Fifty per cent of the population is grey by 50. More women are going grey because of pernicious anemia often linked to dieting, hormone treatments often linked to the pill, and stressful lives. Hair also gets coarser and dry.

Hair biology researchers at the Paris headquarters of cosmetics giant L’Oreal hope they will eventually be able to prevent hair going grey. They have already solved one part of the genetic secret of why hair turns grey on its way to becoming white.

The L’Oreal researchers have discovered how human hair loses its colour. Each hair has cells called melanocytes that act as chemical factories to make two pigments, a red-yellow combination and a brown-black one. Blended in different proportions, these two pigments account for all the shades of human hair.

Experts had believed that hair lost its colour because this pigmentation manufacturing stopped or something blocked the transfer of the pigments into the hair strand.

But L’Oreal researchers found what really happens is a gradual decay and disappearance of the melanocytes. Their results have been published in the British Journal Of Dermatology.

The researchers unexpectedly discovered that the melanocytes in all human hair don’t contain one of three enzymes that were believed to fuel the pigment-making process. And this missing enzyme, called TRP2, might offer protection against the gradual disappearance of the melanocytes that is responsible for greying.

The scientists have concluded that there is a close connection between the greying of human hair and the absence of TRP2. This TRP2 absence implies that the gene responsible for the production of tyrosinase-related protein 2 is switched off in hair, but switched on in skin. So finding a way to switch the gene on in hair melanocytes could be a first step to avoiding grey hair.