Scratching the itch
Q: Does scratching an itch make it itch more?The straight answer: Yes
The facts: Scratching an itch does provide some relief because the scratching creates pain signals that travel to the brain. But it's only a temporary reprieve. Scratching an itch only makes it worse, according to new research reported online last week in the journal Neuron.
In tests on mice, scientists at Washington University School of Medicine in the US state of Missouri have found that those pain signals created by scratching cause the brain to secrete a neurotransmitter that intensifies the itch sensation. The same vicious cycle of itching and scratching is also thought to occur in people.
The neurotransmitter, serotonin, is produced to help control the pain signals. "But as serotonin spreads from the brain into the spinal cord, we found the chemical can 'jump the tracks', moving from pain-sensing neurons to nerve cells that influence itch intensity," says senior investigator Professor Chen Zhou-feng, director of Washington University's Centre for the study of itch.
Serotonin's role in pain control was established decades ago, but this is the first time the chemical messenger has been linked to itching, says Chen.
For the study, the researchers bred a strain of mice that lacked the genes to make serotonin. These mice were then injected with a substance that normally makes the skin itch.
It turned out that they didn't scratch as much as their non-genetically engineered counterparts. But when these mice were injected with serotonin, they started scratching more again.
It's not practical, however, to treat itching by trying to block the release of serotonin, Chen says, because the neurotransmitter is involved in growth, ageing, bone metabolism and in regulating mood.
The best thing to do: try your darnedest not to scratch.