What is the cause of early grey hair in young people?

I have observed that very young people develop grey hair as against the normal situation of grey hair coming with old age. Is there any medical explanation for that?What is the cause of early grey hair in young people?
It is almost always simply a matter of genetics. If your parents and grandparents went gray early - you probably will too.What is the cause of early grey hair in young people?
sometimes when there is dandruff and proper care is not taken to prevent it, they can weaken the roots of hair and the pigmentation too. also high fluorine content present in water used to wash hair contributes to developing grey hair in young people in some countries. (it also leads to skin allergies and loss of bone tissue etc.,) stress plays a key role in early greying of hair along with other factors like genetics and diet.
Genetics and possibly stress.
Things such as stress can effect hair color and general health of hair but a lot of the time it's in your genes.
Genes and diet. But stress can also cause grey hair in many cases
genetics...look at your dad..he'll give you the answer to what your hair will probably be
Stress, genetics, and diet all play a role
Genetics. I started when I was sixteen, and at 26 I am at least 45% white, just like my parents. Its a horrible myth that stress and diet cause this, it is a simple matter of the hair shaft filling with air instead of pigment.