Why does our hair turn gray or white?

Dr. Desmond Tobin, professor of cell biology from the University of Bradford in England, suggests that the hair follicle has a melanogentic clock which slows down or stops melanocyte activity, thus decreasing the pigment our hair receives. This occurs just before the hair is preparing to fall out or shed, so the roots always look pale.

Moreover, Dr. Tobin suggests that hair turns gray because of age and genetics, in that genes regulate the exhaustion of the pigmentary potential of each individual hair follicle. This occurs at different rates in different hair follicles. For some people it occurs rapidly, while in others it occurs slowly over several decades.

In a February 2005 Science article (Nishimura, et al.) Harvard scientists proposed that a failure of melanocyte stem cells (MSC) to maintain the production of melanocytes could cause the graying of hair. This failure of MSC maintenance may result in the breakdown of signals that produce hair color.

There are other factors that can change the pigmentation of hair, making it lighter or darker. Scientists have divided them by intrinsic (internal) and extrinsic (external) factors: