Grey couldn't be trendier; paint your living room grey and parade around in your grey cashmere sweatpants and you'll be living the dream. Entire interior decorating colour charts seem to be devoted to endless shades of grey – certainly more than fifty – but as soon as a single wiry grey hair appears on our scalps most of us react as if we've just been diagnosed with a terrible disease. "What? Where? Pull it out. Quick!"

So, where do those grey hairs come from? Why do they poke through and unsettle our equilibrium? Why does hair turn grey? Can we do anything to stop them?

First, let's take a look at how it happens; the natural inclination, when you see a grey hair, is to assume that one of your normal hairs has suddenly changed colour. One minute, it was happy to be auburn, the next, it has become grey just to spite you. But in fact, it's probably just negligence on your behalf. Maybe you've not been looking closely enough in the mirror because – newsflash! – that grey hair was grey from the start. All hair grows from the follicle, and all hair (that is visible) consists of dead cells. Dead cells can't suddenly change colour, so that annoying little hair must have started out grey. You only noticed it now because it's been growing for a while.

So, what happens in the follicle?

Well, lots of stuff, but in terms of hair colour, the important thing to remember is that the follicles reach a point where they simply stop producing pigment. A hair with no pigment is, for all intents and purposes, white. It only looks grey because of an optical illusion caused by viewing it alongside coloured hairs. But it's white, so you have white hair. Sorry about that.

Why does the pigment stop being produced?

Age; the cells in your skin responsible for producing pigment decide they haven't got the energy to do so anymore. The biological significance of that... we'll leave to biologists. Maybe the pigment is part of a signalling/plumage thing, maybe the cells just lose interest, but that's what happens; the pigment runs dry.

You can think of it as inevitable and perfectly normal – which it is – or you can think of those hair follicles as dysfunctional in the sense that they have stopped functioning in a way you've become used to.

And it's not just a lack of pigment to consider; the hair produced by these 'dysfunctional' follicles is also more fragile than normal hair because the cuticle – the outer lining – is thinner, which means it ends up coarser and more kinked in shape than your other strands of hair. If those grey hairs were sleek, smooth and lustrous you might forgive them. But usually, they're anything but.

The other thing to remember is that because a strand of normal coloured hair doesn't just fade into grey, your grey hairs grow straight from the dysfunctional follicle, so their abnormal shapes are even more apparent when they are short as they stick out; doubly annoying.

Is age the only factor?

It's the biggest factor but genetics can cause premature greying too, which is why some men and women go silver grey in their 20s – and most look great, it has to be said – so your genes will have a big say in when you go grey and how quickly it happens. There's nothing you can do to change your genetics but health and lifestyle is believed to influence greying too, and you can do something about that. Stress, poor diet and smoking may all have an effect on the timing and rate of greying; everyone is different though.

How can you help?

Grey hair is almost inevitable; however, you can make lifestyle changes to eliminate those extra 'risks' – which will help the condition of your hair generally. You can also look after the grey hairs you’ve already got. Show them a little love with gentle shampoos, nourishing conditioners, protective serums and lay off the heated styling tools as much as you can; with all of that, your greys will look better and behave better.

And if you can't bear to see it?

Then a grey cover up is the way to go. There are some great home colour products from Garnier that are specifically formulated for the optimum grey cover up. Permanent hair dye will give you the best and longest-lasting coverage, but you might consider semi-permanent colour for a short period or a root touch-up product to hide those tell-tale signs when your dye starts growing out. Or, maybe it's time to embrace the grey; just think how fashionable you'll be and what better excuse to buy some matching cashmere sweatpants?

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