* Melanin Reduction: Hair color is determined by melanin, a pigment produced by cells called melanocytes in hair follicles. As you age, melanocyte activity slows down and the amount of melanin produced decreases.
* Hydrogen Peroxide Buildup: Our hair naturally produces hydrogen peroxide. An enzyme called catalase usually breaks it down, but as we age, catalase production also declines. The buildup of hydrogen peroxide can bleach the hair from the inside out.
* Genetics: The age at which hair starts to lighten and the extent of the lightening are largely determined by genetics.
The combination of these factors usually results in hair becoming lighter, eventually turning gray or white as melanin production ceases.