This is a hair myth – pulling out one hair does not cause two to grow back in its place. But if the hair is starting to turn white (there is no such thing as grey hair) and you pull one white hair out, it may well be that the neighbouring hair is just about to start growing, so two nearby hairs commonly appear white around the same time. ‘Grey hair’ is only the effect of white hair interspersed with normal, darker coloured hair.
The science bit:
You should never pull out a scalp hair because not only will an additional hair not grow, the hair you pulled out may not be replaced by another hair – particularly with repeatedly epilated hair. There is a disorder called ‘Traction Alopecia’ that is hair loss caused by pulling. A condition commonly seen when women have worn their hair in braids or cornrows for some time; or when hair is tied back very tightly – a style worn by many ballet dancers. This pressure on the soft tissues within the hair follicle causes scar tissue to form, the hair to be forced out, and the prevention of new hair growth from the damaged follicle.