Malnutrition, severe illness or shocks have resulted in cases of white hair, sometimes within a few days or weeks. Heredity plays an important part. You can see people in their 20s who have white hairs mixed with their normal hair. It is usually traceable to parents or grandparents who have had a similar pattern of hair colour change. The hair in these cases is usually coarse or medium coarse in texture.
Old age is the most frequent cause.
As we grow older, many parts of the body economise and slow down. The colour of hair is produced by the amount and proportion of pigments within it. Dark brown hair contains a lot of black-brown and some red hairs. Ash blonde hair will have small amounts of black and some yellow hairs.