As soon as we're born, we're destined to age. Some of us age gracefully - we enjoy years of youthfulness - while others experience hair loss, wrinkles, and greying earlier than expected.
Found in the core of each hair, a
pigment known as
melanin gives rise to a person's hair color. This universal pigment is also found in our skin and eyes, giving use our unique physical traits. Dark and light versions of melanin -
eumelanin and
phaeomelanin, respectively - combine in various combinations to create all natural hair colors.
Melanin itself is the product of a specialized cell, the
melanocyte, which is found in each hair follicle, from which the hair grows. As hair grows, the melanocyte injects melanin into the hair cells, which contain the structural protein
keratin. As long as the melanocytes continue injecting melanin into the hair cells, the hair retains its original color. At a certain age, however, which varies from person to person, the amount of melanin injected is reduced and eventually stops. The hair, without pigment, turns grey and eventually white.
The reason for this decline of production of melanocytes is uncertain. However, a team of Harvard scientists found that the cause was the failure of the melanocyte stem cells to maintain the production of the essential pigments, due to age or genetic factors, after a certain period of time. For some people, the breakdown comes in their twenties; for others, many years later.
According to the site of the magazine
Scientific American, among Caucasians 50 percent are 50 percent gray by age 50. Adult male gorillas also develop silver hair, but only on their backs.