The itch that must be scratched may soon be no more, according to scientists who made an unexpected discovery at a laboratory in America. Researchers at Washington University's medical school in St Louis were hunting genes that govern our ability to sense pain when they stumbled across something quite different: a gene that lets us feel itchy.

The discovery lays down the genetic basis for one of the body's most powerful urges, the ability to writhe in a woolly jumper and occasionally demand that part of us receives instant relief through a good scratching.

Zhou-Feng Chen, who led the study, which is published in the journal Nature, was studying mice bred to lack a gene called GRPR, which was thought to be involved in helping pain signals pass along the spinal cord. It soon became clear that the mice reacted to pain in exactly the same way as normal mice. But later on, the team decided to test the animals' response to substances known to cause itching. They found that while the normal mice began repeatedly scratching themselves with their hind legs, the mice lacking GRPR hardly scratched at all.

Dr Chen said the chance discovery would help drug developers design pills which can block the itchiness pathway. It could dramatically improve the comfort of people with skin disorders such as eczema, and patients taking morphine and other treatments which can cause chronic itchiness as a side-effect, he added.