Question: Why when you are older do you start to get grey hair?

Tess Newman answered on 30 Apr 2012:

Grey/White hair is caused by a lack of pigment – it is this pigment in the first place which causes your hair to have a colour,. As we age, there is a gene within our DNA that stops this pigment creating our hair colour, and so people go grey. There is no set age where this happens, some people go grey while they are still at school, and it doesn’t necessarily happen all over the hair at once. You may have noticed people with a white streak in their hair, and this is just the same process as going grey
There are several theories why this gene has survived in the human population – after all, it doesn’t make you more likely to survive than somebody who has not gone grey! One belief is that it marks out people who are less fertile (due to their age), So that more fertile, younger members of the population would instantly know who would be preferable to have as a mate – i.e. who is more likely to provide them with children. But this is just one theory of many…