Why does hair turn white?
The hair gets color from the hair follicle. If the hair follicle runs out of the color pigment, then the hair turns white.
A single head contains hundreds of thousands of follicles. Each follicle produces a single stand of hair. The follicle contains various different cells, including keratinocytes and melanocytes. The keratinocytes build up keratin, which eventually become the hair, whereas the melanocytes contain a pigment called melanin, which they insert into the keratin. Depending on the genetics, the melanin could be a different color, which is why some people have black hair, while other have blond, red, or brown hair.
Eventually, the melanin within the hair runs out, hence the hair loses the color. Technically, these hairs without color are neither white nor gray, but rather transparent. The hairs appear to be white or gray, depending on how the light reflects from them.
The main reason for the melanin to run out is age. Over time, each follicle stops producing melanin, and as the melanin runs out, the hair turns white. In most cases, the hair will start turning white, around the same time that the hairs of the person’s parents and grandparents started turning white.
However, in some cases, the hair will start turning white before that time. This could be due to a variety of reasons. At times, before the follicle runs of melanin, the melanocytes might start making mistakes, such as depositing the pigment at the wrong place so that it has no effect on the hair. The reason for this is unclear, however research is underway.
Other reasons include exposure to ultraviolet light and chemicals, which can happen due to prolonged exposure to the sun, or chemotherapy. An increased build up of hydrogen peroxide in the follicles, is another reason for white hair. Furthermore, conditions such as thyroid deficiencies, Waardenburg syndrome or a vitamin B12 deficiency can also result in white hair.