It is something that has made scientists scratch their heads for years and now the University of Sussex has the answer.
Scientists from the university have joined with colleagues at the University of Hull to look at why itching is contagious.
The team discovered the part of the brain responsible for the itching and why some people are more prone to it than others.
Psychology lecturer Dr Henning Holle and researchers from the University of Sussex and Brighton and Sussex Medical School wanted to determine why some people are particularly vulnerable to itchiness when they see others scratching.
Volunteers filled in personality questionnaires and then underwent scans while being shown short videos of people either tapping or scratching their arms and chest.
The results showed while contagious itch is experienced by most – around two-thirds of those involved in the study actually scratched themselves while watching the video – the people who experience more negative emotions are more susceptible than others.
The researchers matched the volunteers’ tendency to scratch with activity in several brain regions previously identified as part of the “itch matrix”.
The activity noted in three specific regions of the brain could be linked to subjective ratings of itchiness.
It is hoped this new information could be used to help people suffering from chronic itching sensations where there is no underlying cause.
Dr Holle 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’.”
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