But researchers found that when the body gets stressed – such as by serious illness or from some other shock – this has a dual effect.
Scientists have found stress really does make you a silver fox, like George Clooney or Philip Schofield.
It has been argued that going grey early is an inevitable genetic process that runs in families.
As well as our immune system mounting a defensive response, it also triggers changes in the cells in hair follicles which produce colour.
For example, TV presenter Philip Schofield has said he first started going grey at 16. George Clooney said he first started going grey at 33
This in turn makes our hair turn silvery or grey.
Researchers from the University of Alabama, Birmingham found the ‘surprising’ link between genes that control hair colour and genes that signal to our bodies it is time to fight off an infection.
As well as ‘turning off’ hair colour, it can also turn off colour in the skin – leading to the disease vitiligo, of which pop star Michael Jackson was a famous sufferer.
The research – carried out on mice – published in PLOS Biology reports when the body is under attack our cells produce chemical signals called interferons.
These interferons make our cells’ machinery undergo changes that thwart viruses and generally boost defences.
But the unexpected side effect of the defence system is that it turns off cells that produce hair colour.
WHY DOES HAIR GO GREY?
Grey hair is hair without pigment, and it could be regarded as the hairs’ ‘natural state’.
When we are young, our hair is coloured by the pigments produced by cells in the hair follicle known as melanocytes.
As we grow older, the melanocytes gradually become less active, so less pigment is produced, the colour fades, and grey hair grows instead.
There’s nothing you can do to stop yourself going grey – it’s just a part of growing older.
William Pavan, study co-author and researcher at the National Institute in Health said: ‘This new discovery suggests that genes that control pigment in hair and skin also work to control the innate immune system.’
He added: ‘These results may enhance our understanding of hair greying.
‘More importantly, discovering this connection will help us understand pigmentation diseases with innate immune system involvement like vitiligo.’
Vitiligo, which causes discolored skin patches, affects between 0.5 percent to 1 per cent of all humans.
Claims that hair can turn white or grey overnight, are not supported by science.
Legend has it that Marie Antoinette’s hair turned white overnight – appearing white on the day of her execution.
Scientists have said this story is unlikely – as there is no mechanism that could explain how hair – which is biologically dead – could become altered by a biological process in the body.
In Marie Antoinette’s case it has been claimed that her hair was grey all along, and she just appeared without her wig.
It is likely that some people are genetically more likely to go grey early, however.
For example, TV presenter Philip Schofield has said he first started going grey at 16. George Clooney said he first started going grey at 33.
Last year, researchers from University College London found the first individual gene that causes hair known to turn grey called IRF4.