Folklore has it that a fright or fear can cause a head of hair to turn from youthful hues to silvery white overnight.
Marie Antoinette and Sir Thomas More were both reported to have had their hair turn grey just before their executions.
It has long been speculated that Marie Antoinette and Sir Thomas More may both have suffered from a medical condition called alopecia areata in which large amounts of one type of hair can suddenly fall out.
Research in mice has shown that chronic stress causes DNA damage that could lead to conditions like greying hair.
Greying hair can be reversible
Now researchers at Columbia University Vagelos College of Physicians and Surgeons indicate that this greying through stress may actually be reversible.
'Understanding the mechanisms that allow 'old' grey hairs to return to their 'young' pigmented states could yield new clues about the malleability of human ageing in general and how it is influenced by stress," says senior author Martin Picard, associate professor of behavioural medicine at Columbia University Vagelos College of Physicians and Surgeons
Picard explains: ‘Just as the rings in a tree trunk hold information about past decades in the life of a tree, our hair contains information about our biological history. When hairs are still under the skin as follicles, they are subject to the influence of stress hormones and other things happening in our mind and body. Once hairs grow out of the scalp, they harden and permanently crystallise these exposures into a stable form.’
Ayelet Rosenberg, first author on the study and a student in Picard's laboratory, developed a new method for capturing highly detailed images of tiny slices of human hairs to quantify the extent of greying in each of those slices. Each slice, about 1/20th of a millimetre wide, represents about an hour of hair growth.
Greying hair compared with stress levels
Under a high-resolution scanner, researchers noted variations in hue of the hair of 14 volunteers, who also kept a stress diary.
The investigators immediately noticed that some grey hairs naturally regain their original colour.
The hairs were were compared to stress diaries. It was noted that an alleviation of stress corresponded with hairs regaining pigment.
"There was one individual who went on vacation, and five hairs on that person's head reverted back to dark during the vacation, synchronized in time," Picard commented.
The mitochondria connection
The evidence suggests stress-induced changes in mitochondria (the so-called "powerhouses" of cells) may explain how stress turns hair gray.
Picard explains: ‘Mitochondria are actually like little antennas inside the cell that respond to a number of different signals, including psychological stress."
The mitochondria connection between stress and hair colour differs from that discovered in a recent study of mice, which found that stress-induced greying was caused by an irreversible loss of stem cells in the hair follicle.
'Our data show that greying is reversible in people, which implicates a different mechanism," says co-author Ralf Paus, PhD, professor of dermatology at the University of Miami Miller School of Medicine. "Mice have very different hair follicle biology, and this may be an instance where findings in mice don't translate well to people.'
Does this mean an end to hair dye?
So does this mean we can look forward to throwing away the hair dye? Not so fast.
Picard says: ‘We think hair needs to reach a threshold before it turns grey. In middle age, when the hair is near that threshold because of biological age and other factors, stress will push it over the threshold and it transitions to grey.
‘Unfortunately, reducing stress in a 70-year-old who's been grey for years won’t darken their hair. And increasing stress in a 10-year-old will be enough to tip their hair over the grey threshold.’