Some people get grey (or white) hairs in their twenties, and others still have dark hair well into their seventies and eighties. The process of greying can occur gradually over many years as individual hair follicles stop producing colour, or it can happen within a matter of months or a few years. How long depends a lot on genetics. Also, our changing hair colour depends on how dark the rest of the hair is to begin with.

 How it Happens

Individual hairs don’t actually “turn” grey-they grow in that way.

In fact, individual hairs don’t actually “turn” grey-they grow in that way. Every day, hairs fall out and new ones emerge in their place

.

As the hair grows in the follicle, colour is deposited into the new growth in the form of two substances, eumelanin and pheomelanin, which all people have in varying quantities…

When one of your follicles stops producing these coloured pigments (usually with age), the next hair growing out of that follicle will grow in grey.

 But, Why Does this Happen ?

Why this happens is one of the mysteries of ageing. Having grey hair doesn’t mean a person is not healthy.

A number of external causes can make hair grey. According to most sources, smoking is a big reason. People who smoke are four times more likely to be prematurely grey. (Some evidence, by the way, links smoking to early baldness, too.) Early greying (or balding, for that matter) is not a sign of early ageing. Despite some reports, no solid link has been found.

Most people, especially those with dark hair, will begin to notice a few white hairs by their late twenties or early thirties.