Sight of itching: scratching can be contagious


A British study by researchers at Hull University found that scratching can be contagious to neurotically sensitive people. When they see them "that someone is scratching their skin, they have to scratch themselves," according to the scientists. It may now be possible to explain why some people suffer from constant itching, although no skin disorders can be diagnosed.

Scientists have known for a long time that scratching, like laughing or yawning, can be contagious. So far, the relationships have not been clearly proven with regard to the phenomenon of “itchy rash”. Because not everyone has to scratch their skin immediately if their counterpart is itchy. During an experiment, scientists from the University of Hull found that not all, but only certain people, are significantly more susceptible to this. "Particularly emotionally unstable people themselves experience an itch when they watch a person scratch". According to researchers, just observing activates certain regions in the brain that are also activated when itching itself. It is possible that excessive activation in the brain, a kind of “scratch matrix”, is responsible for the constant itching. Many people experience the itching, although a dermatologist could not find any organic cause, as the research team wrote in the journal "PNAS".

Scratch films caused 60 percent to itch. In the course of the study, the 33 male and female participants were shown video clips in which people scratched themselves or even tapped certain parts of their bodies. During the viewing, the test subjects were filmed without their knowledge. After each video sequence, the participants should judge for themselves how much it itched. Initially, it was found that the test persons felt itching more when scratching than when watching the knock. Over 60 percent got infected by scratching and itched themselves in at least one of the video films. The researchers write in their study report, especially if the left upper arm was scratched in the video, which led to the itching.

Neuroticism made it more susceptible to itching Later on, it turned out that people are obviously more prone to itching if they are more susceptible to neuroticism. Neuroticism (derived from neurosis) is a specific personality trait in which people are more susceptible to negative emotions from their environment or stress. The scientific team was unable to find any differences between women and men. The contagious effect was the same for women and men. "Surprisingly, the ability to empathize did not matter," said study director Hennig Holle. Subsequent tests showed that people who were particularly prone to itching had no greater ability to empathize or sympathize than others who were less likely to be infected by scratching.

In the third step, the scientists had some of the study participants watch videos while a computer tomograph (MRI) scanned the activities of the brain. Numerous areas of the “scratch matrix” were activated. The regions were particularly strongly activated among the “neurotic participants”. The specific areas of the brain are particularly stressed when simulations of activities are carried out in the brain or chemicals on the skin cause itching. This shows that "the same areas in the brain are used in organic and psychological itching," says the team.

Activation of the scratch matrix triggers for psychological itching "We assume that the activation of the central scratch matrix can trigger triggers for psychogenic itching diseases", the researchers sum up in the "Proceedings of the National Academy of Sciences" (doi: 10.1073 /pnas.1216160109). "Subjects with a higher neuroticism score were significantly more often infected by itching." This could probably explain why some patients suffer from constant itching, even though there are no organic skin diseases and the skin is not irritated. Accordingly, it may be that the “itch matrix” reacts over-sensitively to those. Further research now needs to clarify which functions individual areas of the brain have and how the findings in the treatment of psychological itching could be incorporated. (sb)

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