While you can already see a lot of gray hair, your girlfriend who is four years older has nothing to do with it. Why is it so unfairly distributed?
The biggest cause of gray hair is heredity. The genes you get from your parents largely determine how quickly your hair ages. There is a good chance that you will go gray at the same age as your father or mother.
Read also: Can you get gray hair from stress?
According to the Northwestern University Feinberg School of Medicine, at some point the hair follicle stops sending signals to cells that color your hair, causing your hair to lose pigment and appear gray (actually white). It's a myth that this happens overnight. The hairs you already have do not fade, only new hairs grow grey.
