Study reveals how brain tells you to stop scratching

A team of scientists from the University of Louvain in Belgium has discovered a vital process which helps your brain understand that you’ve scratched enough, an achievement that may revolutionise the treatment of millions of patients who suffer from chronic skin conditions such as eczema and psoriasis.

The culprit is a protein named TRPV4, an ion channel which serves as a gatekeeper for sensory nerve fibres. Scratching an itch causes TRPV4 to send negative feedback to the spinal cord and the brain, telling them that enough has been done.

Without this signal, scratching continues uncontrolled, which may explain why chronic itch sufferers become trapped in relentless scratching cycles.

"When we scratch an itch, at some point we stop because there's a negative feedback signal that tells us we're satisfied," explained Roberta Gualdani, who led the research. "Without TRPV4, the mice don't feel this feedback, so they continue scratching much longer than normal."

Gualdani's team developed genetically modified mice which only disabled TRPV4 through sensory neurone deletion. The researchers used genetic testing together with behavioural assessments to study mice which developed chronic itching symptoms that matched atopic dermatitis.

The mice without TRPV4 scratched themselves infrequently, but the duration of each bout was very long compared with usual conditions. This wasn't contrary; rather, it demonstrated one basic fact: that TRPV4 doesn't just generate itchiness; it is responsible for initiating the process telling your body to stop.

TRPV4 has two functions: when it acts on skin cells, it produces itchiness, and when it acts on neurones, it determines and regulates how much scratching occurs. "Broadly blocking TRPV4 may not be the solution," says Gualdani. "Future therapies may need to be much more targeted, perhaps acting only in the skin without interfering with the neuronal mechanisms that tell us when to stop scratching."

Chronic itch affects millions worldwide, yet treatment options remain severely limited.