Itching and scratching a 'vicious cycle', say researchers
Research into itching has indicated why scratching can paradoxically make you feel more itchy.
A study in mice found that "scratch cycles" get harder and harder to break because of serotonin released into the system.
The research, which has not been tested in humans, indicates that blocking specific serotonin receptors in the spine could reduce chronic itching.
Dermatologists said the research could help towards effective itch control.
Itchy and scratchy
Itchiness can be caused by a number of factors, ranging from very minor irritation by dust and small hairs to serious skin conditions.
One of the purposes of scratching is to produce pain. This disrupts the itch by getting nerves to carry pain signals instead of itch signals.
The pain causes the "happy" neurotransmitter serotonin to be released by the brain, to control the pain.
But the serotonin then activates spinal cord nerve cells that control itch intensity when it reaches the spine, according to Prof Zhou-Feng Chen, director of Washington University's Center for the Study of Itch.
"In mice, there is a vicious itching [and] scratching cycle," Prof Chen said. "If you reduce the serotonin the itchy intensity reduces."
Prof Chen said it was not feasible to block serotonin release, because that could have wide-ranging consequences. Serotonin is involved in growth, ageing, bone metabolism and in regulating mood.
The research indicated that one of the most promising ways of controlling chronic itching is to disrupt the interaction between serotonin and cells that relay itch signals to the brain, Prof Chen added.
A spokesman for the British Association of Dermatologists said the research could help better understanding of the itch mechanism, and ultimately could help the development of treatments for chronic itching.
"More effective ways of managing itch... would be hugely comforting for people with a wide range of conditions," he said.