Why does your hair turn gray?

A curious child asked her mother:

gray hair 1

The mother was a little offended. But then she would use this occasion to teach her child:

gray hair 2

The mother was was very satisfied with her answer, thinking that the child now got something to think about. But the child responded quickly:

© Copyright: W.Bøe / multiart.no
© Copyright license: W.Bøe / multiart.no