Hydrogen peroxide lightens, or bleaches, human hair. People with blonde hair typically use it to lighten their locks, particularly in the winter months when there isn't a lot of sun.
While hydrogen peroxide has been used for years to lighten hair color, research by a team of European scientists found that the natural build up of hydrogen peroxide within the hair follicles turns the hair gray.
The hydrogen peroxide builds up over time due to wear and tear on the hair follicles. Due to this build up, the body is unable to produce the enzyme necessary to support the production of melanin. Melanin is responsible for hair color and, without it, hair takes on a gray color.