white hair
white hair
(Image credit: I Love Images/REX/Shutterstock)

The notion of hair turning 'white with fright' overnight may not be a myth after all. Reported victims of 'canities subita' (or sudden whitening) include Mary Queen of Scots, whose hair allegedly turned white the night before her beheading, at the age of 44, and Marie Antoinette, whose lady-in-waiting reported that the 35-year-old queen's hair "had become, in one single night, as white as that of a woman of seventy" in 1791, amidst the tumult of the French Revolution.

The medical profession has been quick to dismiss these stories as historical fantasy or, at the very least, exaggeration. Stress is thought to accelerate the whitening process, but over a period of weeks, months and years - not hours. Take the case of Captain Eric Moody, an airline pilot who successfully made an emergency landing after a plume of volcanic ash put all four of his plane's engines out of action. Within a year, his hair was completely white. Severe or chronic stress may cause DNA damage which affects the pigment-producing system within the follicles, or the enzymes which break down the hydrogen peroxide which, in older age, literally bleaches hair from the inside out.

However, doctors argue that it is medically impossible for hairs which have already formed to change colour. They believe that so-called overnight whitening can be explained by an autoimmune response called alopecia areata, in which stress causes sudden hair loss. This form of alopecia often targets pigmented hairs, leaving white hairs intact. But how can this explanation account for those in their twenties and thirties who claim to have made an overnight transition from a full head of dark hair - with no visible greys - to a snowy white mane, with no discernible loss in thickness?

More than 100 known cases (14 witnessed by a doctor) of canities subita have been reported over the past 200 years. These include the case (reported by the British Medical Journal in 1902) of the 22-year-old woman who witnessed another woman's throat being cut. By the following morning, the pubic hair on the right side of her body had turned white. Then there's the case (reported in Scientific American in 1915) of the 23-year-old French soldier who survived a mine explosion, only to wake up in hospital the following morning to white tufts of hair on the left side of his head. Most recently, journalist Anne Jolis reported that her upper lip hairs turned white after she misinterpreted celebratory gunfire as something more sinister whilst travelling abroad. "My moustache is as thick as it's ever been," she insists. "And it was sparse enough before the incident that I would have noticed any white hairs that were already there."

Scientists, who have also reported on at least two known cases of spontaneous reversals of hair whitening, may be at a loss for an explanation, but it appears that there may be life in the old wives' tale yet...