Even thinking about other people scratching makes us spontaneously break out in an itchy feeling all over our bodies.
In fact, this article could make for a long read.
Now scientists have worked out why humans can’t bear to watch other people deal with an itch without contagiously wanting to scratch ourselves, and it isn’t empathy.
The study, from the Washington University School of Medicine, found that (like yawning) the pattern of behaviour is actually hardwired into the neural circuits of our brain.
Meaning that if one person in a group starts doing it, it is a contagious response that we cannot control.
Principal investigator Zhou-Feng Chen said: “Sometimes even mentioning itching will make someone scratch. Many people thought it was all in the mind, but our experiments show it is a hardwired behaviour and is not a form of empathy.”
The team made mice, who are renowned for their poor vision, watch a video of another mouse scratching on a computer screen.
Chen said: “Without a few seconds the mouse in the enclosure would start scratching too.”
They then went on to identify the source of this behaviour, the suprachiasmatic nucleus (SCN) in the brain, which released a chemical GRP – known to be a key transmitter of itch signals between the skin and spinal cord.
“The mouse doesn’t see another mouse scratching and then think it might need to scratch too. Instead its brain begins sending out itch signals using GRP [the chemical] as a messenger.”
And when the team blocked GRP receptors in the brain the mice did not scratch when watching another animal deal with an itch, Chen said: “It’s an innate behaviour and an instinct.”
Remember that next time you just can’t suppress the urge to have a good old scratch.