ffs. Grey hair has fuck all to do with how long you sit on your fucking arse.
Hair color is the follicles due to two types of melanin, eumelanin and pheomelanin. Generally, if more melanin is present, the color of the hair is darker; if less melanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color.
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Grey or white hair is not actually a true grey or white pigment. In fact, it is clear due to lack of pigmentation and melanin. The clear hairs appear as Grey or White because of the way light reflects from the hairs. Grey hair color typically occurs naturally as people age (see "Effects of aging on hair color", below). For some people this can happen at a very young age (for example, at the age of 10). The same is true for white hair. In some cases, grey hair may be caused by thyroid deficiencies or a deficiency of B12.[7]
The Journal of Investigative Dermatology published a study in 2005 which found that white people will begin to grey in their mid-30s and Asian people begin greying in their late thirties, but most black people can retain their original hair color until their mid-forties.[8] People with albinism may have white hair due to low amounts of melanin.
http://en.wikipedia.org/wiki/Human_h...and_white_hair
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