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Scientists Have Worked Out Why Scratching Makes You Itch More

Chimpanzees at Taronga Zoo. Cameron Spencer/Getty Images

Scratching at an itch really does only makes it worse.

Research by scientists at the Washington University School of Medicine in St Louis indicates scratching causes the brain to release serotonin which intensifies the itch sensation.

The findings, in mice, are reported in the journal Neuron.

The same vicious cycle of itching and scratching is thought to occur in humans and the research provides clues which may help break that cycle, particularly in those who experience chronic itching.

Scientists have known for decades that scratching creates a mild amount of pain in the skin, says Zhou-Feng Chen, director of Washington University’s Center for the Study of Itch.

That pain can interfere with itching, at least temporarily, by getting nerve cells in the spinal cord to carry pain signals to the brain instead of itch signals.

“The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain,” Chen says.

“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.”

Scientists uncovered serotonin’s role in controlling pain decades ago, but this is the first time the release of the chemical messenger from the brain has been linked to itch.

Serotonin is involved in growth, ageing, bone metabolism and in regulating mood.

Antidepressants such as Prozac, Zoloft and Paxil increase serotonin levels to control depression.

Chen says it might be possible to interfere with the communication between serotonin and nerve cells in the spinal cord.

Those cells relay itch signals from the skin to the brain.

“We always have wondered why this vicious itch-pain cycle occurs,” Chen says.

As his team works to better understand the molecular and cellular mechanisms that control the cycle, Chen suggest that those who itch pay attention to to their mother’s advice and try not to scratch.

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