Stress can turn your hair grey, but finding ways to chill out can sometimes restore your locks to their natural colour. A team of researchers at Columbia University examined the way that human hair loses its colour when a person is under stress, and found that for many it’s only temporary, which can be reversed by something as simple as taking a holiday. Unfortunately not everyone is capable of this ‘repigmentation’, though, and the longer you’ve been grey, the less likely it is that your hair will return to its natural state.