Here's how hair turns white in humans:
* Melanin: Hair gets its color from a pigment called melanin. There are two types: eumelanin (brown/black) and pheomelanin (red/yellow).
* Graying: As we age, the cells that produce melanin (melanocytes) in hair follicles start to produce less melanin, or stop producing it altogether. This results in the hair losing its color and appearing gray.
* White: When a hair follicle completely stops producing melanin, the hair appears white.
There are also other factors that can contribute to graying, such as genetics, stress, and certain medical conditions.