Why hair turns white
To begin with, there are two parts to the hair: the shaft and the root. The shaft is the coloured part of the hair whether it is brown, black, red or blonde. The root keeps that piece of hair fixed on the scalp.
Under the root of each hair is a follicle. It surrounds the hair's root. Each hair follicle contains a number of pigment cells. Melanin is constantly produced by these cells. These cells are responsible for giving the hair its colour.
Melanin is also responsible for the pigment of our skin and eye colour. Darker skinned people have more melanin in their skin than those with lighter skin. It also determines how quickly a person will burn or change colour when exposed to the sun's rays.
As you get older, the pigment in your hair follicles gradually die. There will come a point where melanin is not produced anymore. Hence, the colour of the hair changes at the root to a lighter colour whether it is silver grey or white.
From the time your hair starts turning white or grey, it will take about 10 years before your entire crown will turn into this colour.