Researchers have shown that the sensation of an itch can be caught visually in the same way as yawning.
It is a phenomenon that can leave entire rooms full of people scratching at the merest mention of fleas or lice. Now scientists have proven for the first time that itching really can be contagious.
In a condition known as itch transmission, the researchers have shown that the sensation of an itch can be caught visually in the same way as yawning.
They found that simply watching a video of someone else scratching was enough to induce and intensify itching in volunteers.
Even when they were given a few drops of a liquid designed to induce itching on a patch of their skin, the volunteers tended to scratch more on random parts of their body.
Dermatologists at Wake Forest University School of Medicine in North Carolina believe itching becomes contagious because the brain becomes hypersensitive when someone nearby scratches and so misinterprets any kind of physical sensation on our skin as an itch.
Dr Gil Yosipovitch, who led the research which is published online in the British Journal of Dermatology, said: “Although it’s a well-known sensation and dermatologists often feel itchy after seeing their patients scratch, contagious itch has not been studied systematically at all.
“Our results suggest there must be a central brain mechanism responsible for the generation of the itch sensation in the absence of itch stimuli. It is possible that sensory inputs from various regions, not specifically related to itch, may be wrongfully interpreted as being “itchy”.
“It appears that there is low threshold for ‘feeling an itch’ when this suggestion appears in a visual form, or even by simply thinking/reading about it.”
The researchers asked 25 volunteers to watch a series of five minute video clips that ether showed people scratching their left forearm or sitting idly.
They were either given a solution of histamine to induce itching on a patch of their skin or a few drops of harmless salt solution.
The volunteers tended to scratch twice as much when watching someone else scratching on the video compared to the video of the person doing nothing. The sensation occurred both in healthy volunteers and patients who suffered from atopic dermatitis.
The scientists also found that even when the histamine liquid was used, tended to scratch at other points in their body rather than just where the liquid had been applied.
Similar work in primates has also shown that monkeys can catch itches too and the researchers now believe contagious itching may be rooted in our evolutionary past as we evolved to live in close knit social groups.
Growing sensitive to itching when one member of the group is scratching could help to identify parasite infestations early and help to stop them spreading.
The scientists now hope to use their findings to develop new ways of treating people who suffer from chronic itching and skin diseases.
Dr Alexandru Papoiu, another of the researchers behind the study, said it appeared the mechanisms that create the sensation of itching was working “overtime” in these patients.
He added: “It is particularly interesting why humans are “vulnerable” or suggestible to cues of itch.
“If we can understand the underlying mechanism and its cause, we should have a better chance to treat itch, targeting the central nervous system stations involved.”
Nina Goad, from the British Association of Dermatologists, said the study showed how much influence the mind could have on physical sensations.
She said: “This is a fascinating study looking at the power of the mind over a very physical sensation like itch.
“Many people can identify with the idea that watching other people scratch an itch leads you to feel the itch sensation yourself.
“To see this demonstrated in a clinical setting, with a view to developing treatments for common skin diseases like eczema that cause itch, is very interesting.”