Asked by: Angela Smith, Southampton
Going grey is the result of reduced amounts of melanin in the hair, a pigment found in almost all organisms, not just in humans. It is the same compound that tans your skin in response to sunlight. In one form, eumelanin, it results in brown or black hair, while pheomelanin is responsible for red hair and freckles. These are produced in special cells called melanocytes that are found within the hair follicles in the skin.
As people get older, their melanocytes become less active and produce less and less melanin, until they finally die and are not replaced. Hairs then grow without any colouring and are transparent. The age at which people turn grey varies widely. Most of the difference is genetic, but other factors such as poor nutrition, smoking and certain diseases can cause premature greying. Even a terrible shock can sometimes cause hair to go grey quickly.