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Why Nothing Relieves an Itch Like Scratching

New research looks to identify nerve cells to target with new anti-itch medication.

Scratching an annoying itch is one of life’s simple pleasures, but why it provides such profound relief has long been a mystery. Researchers are now homing in on some answers.

Antihistamines can relieve the kind of itching caused by mosquito bites or poison ivy, but scientists want to find ways to relieve the unbearable itching caused by illnesses such as cancer or liver disease. “Antihistamines don’t help most of the hundreds of conditions that can cause chronic, untreatable itch,” says neuroscientist Glenn Giesler of the University of Minnesota in Minneapolis.

Scratching, however, offers an “aah . . . ”

But why? Giesler and his colleagues found that scratching sends a signal from nerve cells in the skin to specialized nerve cells in the spinal cord, which then tell the brain to turn off the itching.

To tease out how it works, scientists sedated monkeys and injected histamine into their lower legs to produce an itch. In response, the spinal cord nerves fired electrical signals, which the scientists could hear through speakers set up in the lab. “It sounds like a Morse code of the nervous system,” Giesler says. They then scratched the leg with an instrument that simulates monkey fingers. The spinal cord nerves fell silent.

“If we can discover a way to mimic the relief that scratching provides, we could get around the destructive effect that constant scratching has on the skin,” says Yale University neurobiologist Robert LaMotte, who was not involved in the study. “This research identifies the nerve cells to target with new anti-itch drugs.”

The study was published online in the journal Nature Neuroscience on April 6.

Nissa Simon, who lives in New Haven, Conn., writes about nutrition and medical issues.

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