One of the most concerning hair problems faced by many is grey hair. In the past, a lot of studies have stated that premature grey hair can be caused by stress, which has been unclear until now. A recent study by a team of Harvard University found out that stress does have a link. It can activate nerves that are a part of the fight-or-flight response.
“Normally, the sympathetic nervous system is an emergency system for fight or flight, and it is supposed to be very beneficial or, at the very least, its effects are supposed to be transient and reversible,” said Ya-Chieh Hsu, a stem cell biologist at Harvard University who led the study.

This link has now proven that stress can be a major factor causing grey hair. In the study, researchers exposed mice to many stress factors, which ended up with grey hair. Scientists also researched on the stress hormone cortisol. A study was done on some of the mice, by removing their adrenal glands to stop cortisol's production. Even after this experiment, it was noted that the hair turned grey under stress. The study concluded that stress causes the activation of sympathetic nerves, which leads to greying of hair.
By activating the nerves, stress can deplete the number of melanocyte stem cells, which are found hair follicles. These cells determine the colour of the hair. When the supply of these cells is low, hair turns grey or white with ageing.