Grey hair happens because the cells that give the hair it’s colour stop making the pigment. This is a symptom of the cells being old or damaged. Age can cause it, but stress also causes damage (or premature aging) in some cells.
What is interesting is why ginger people hair goes white instead of grey!!? Well I find it interesting! It is all to do with the pigments which make up the colour of our hear. What happens when we age as there is a little bit of damage to DNA. This is very normal. These conditions makes things break down. It is called ‘stress’. So funnily enough, sometimes when we get stressed, a similar response can happen and the pigment breaks down.