A new study suggests that itching may be spread from person to person, and like yawning and coughing, scratching is a behavior that is highly contagious.
Lead author Dr. Henning Holle and his team of researchers from the University of Sussex and Brighton and Sussex Medical School have identified the area of the brain responsible for the "contagious" itching, as well as why some people are more susceptible to it than others.
Previous research suggests that the contagious nature of itching was a result of empathy, with people mimicking other's behavior as a form of social bonding.
However, Holle and his team found that contagious scratching was significantly more associated with neuroticism or the tendency to have negative emotions.
Holle and his team asked 51 participants to complete personality questionnaires before scanning their brains as they viewed videos of people scratching or tapping parts of their arms or chest.
The study, published in the Proceedings of the National Academy of Sciences journal, found that while itching was "contagious" among two thirds of the participants, contagious scratching was more common among people with high levels of neuroticism but not those with high levels of empathy.
"Almost everyone has felt that urge to scratch when watching someone else, but no one has ever really known why," Holle said in a news release.
"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," he said.
Based on brain scans, researchers also found that watching other's itch triggers brain activity in the anterior insular, primary somatosensory area, and the prefrontal and premotor cortices. Researchers said that these three regions are part of the previously identified "itch matrix". They said that the regions also become activated when a person actually feels an itch, suggesting that watching someone itch makes the brain think that it is experiencing an 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," Holle said.