Why Scratching Makes You Itch More, Explained By Science

The news: Anyone who's been plagued by mosquitoes or suffered through chicken pox remembers being told by their parents that scratching an itch only makes it worse. Well, new research confirms you should have heeded that sage advice.

According to a study published in the journal Neuron, researchers at the Washington University School of Medicine in St. Louis found that scratching an itch makes your brain release the neurotransmitter serotonin, exacerbating the itching sensation even more.

"We always have wondered why this vicious itch­-pain cycle occurs," senior investigator Zhou-­Feng Chen said in a statement. "Our findings suggest that the events happen in this order. First, you scratch, and that causes a sensation of pain. Then you make more serotonin to control the pain. But serotonin does more than only inhibit pain. Our new finding shows that it also makes itch worse by activating GRPR neurons through 5HT1A receptors."

Source: Washington University School of Medicine

How does it work? When you scratch an itch, it causes minor pain on your skin, forcing the nerve cells in your spinal cord to carry pain signals instead of itching signals. But while that may provide temporary relief, it actually sets off a vicious cycle that irritates your skin even more.

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

To test the theory, researchers bred a special strain of mice that lacked the ability to produce serotonin. When they were injected with an irritant, they didn't scratch as much as other mice. But when they were injected with serotonin, they scratched their itch just as much as others.

What does this mean for humans? Unfortunately, blocking serotonin production is not a viable option for people. The neurotransmitter plays an important role in growth, aging, regulating mood and controlling depression. Messing with serotonin levels would have serious consequences throughout the body, and that trade-off is simply not worth it.

Still, this research opens other possibilities: The study found that blocking the serotonin receptors that activate the neurons associated with itching is a promising way to reduce itching. Oh, and it serves as a reminder you really shouldn't scratch that itch if you want to escape the vicious cycle.

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Eileen Shim

Eileen is a writer living in New York. She studied comparative literature and international studies at Yale University, and enjoys writing about the intersection of culture and politics.

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