London - It is more contagious than yawning or laughter.
Watching someone else itch is likely to cause two-thirds of people to have a good scratch themselves.
Now scientists think they have solved the mystery of why itching is so infectious. It is, they say, all down to how we experience emotions.
The researchers found people who are prone to contagious scratching are also more susceptible to negative feelings.
However, the more emotionally stable the individual, the better they are at suppressing the need to itch when viewing others.
Understanding how the process works could lead to better treatments for severe itching, including eczema, which affects up to six million Britons.
It could also be used to help those who suffer from chronic itching sensations where there is no underlying dermatological cause.
Psychology lecturer Dr Henning Holle from the University of Hull said: “Almost everyone has felt that urge to scratch when watching someone else, but no one has ever really known why.
“It had previously been thought that empathy was responsible. But we found that neuroticism - a measure of the tendency to experience negative emotions - was positively linked to contagious itch.”
Highly neurotic people are known to be highly emotionally reactive and vulnerable to stress.
“We found that participants with higher neuroticism scores are also the ones that are more easily ‘infected’ by contagious itch.
“Our observed link between activity in prefrontal cortex and neuroticism might reflect that the emotionally more stable participants, with low neuroticism scores, are less susceptible to contagious itch, because they are better at suppressing the irrelevant itch sensation arising from observing someone scratch themselves.”
Working with a team of researchers from the University of Sussex, Dr Holle had 51 volunteers fill in personality questionnaires.
They then underwent MRI scans while being shown short video clips of people either scratching or tapping parts of their arms or chest to shed light on how scratching affects the brain.
The scans showed that observing someone scratch activated the same regions of the brain linked with feeling of itchiness when it is caused by an irritant.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), found itching was infectious among 64 percent of the volunteers, with the degree of contagion tied to differences in neuroticism - the tendency to experience negative emotions - as determined by the personality tests.
It had previously been thought that empathy was the reason behind contagious itching.
Earlier research has found that laughter is socially infectious for almost half of people, while yawning affects around the same percentage of individuals. - Daily Mail