A woman's genes are much more likely than lifestyle factors such as stress or diet to cause greying hair, a study suggests.Unilever scientists studied more than 200 identical and non-identical Danish twin sisters aged between 59 and 81.The scientists found little difference between the greyness of the identical twins - who share the same genes.But there was more difference between non-identical twins, whose genes differ, the study found.The study, published in the journal PLoS One, also suggests receding hair is linked to mainly genetic factors.But it indicates hair-thinning on the top of the head is connected to environmental and lifestyle factors.On the issue of greying hair, lead researcher Dr David Gunn said although many theories had been put forward to explain different rates of greying, there was little hard scientific evidence to back them up.Non-identical twinsThere were more differences among non-identical twinsHe said: "This study offers us a fascinating insight into the reason why women go grey and it certainly suggests that environmental factors are not as important as we once thought."The research indicates that irrespective of how stressful a woman's life is, there are greater forces at play which are more likely to cause her hair to grey."Nina Goad, of the British Association of Dermatologists, said previous work had also found few identifiable environmental factors among people who went grey much earlier than their relatives."This means that for the majority of people, greying hair is not down to something you have done, but to genetic factors beyond your control, and that generally your lifestyle will not greatly impact on when your hair loses its colour," she said."There are of course exceptions to this rule."Dr David Fisher, of the Dana Faber Cancer Institute, who had has conducted research into greying, agreed that genetics probably played a key role in controlling when hair turned grey.However, he said there was also some evidence to suggest exposure to certain types of chemical could also promote greying.Source: BBC