It feels good to scratch an itch, but soon afterward the itch sensation feels stronger than it was before.

Now, new research from researchers at Washington University School of Medicine in St. Louis reveals why this is.

According to researchers, scratching causes the brain to release serotonin, which exacerbates the feeling that the itch needs to be scratched. Researchers believe that their findings may help people who deal with chronic itching.

Scientists have long known that scratching generates a benign amount of pain in the skin.

“The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain,” said senior investigator Zhou-Feng Chen, PhD, director of Washington University’s Center for the Study of Itch, in a statement. “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 bred a strain of mice that did not have the genes to create serotonin. When those mice were injected with a substance that usually makes the skin itch, the mice didn’t scratch as much as the control mice. However, when the specially-bred mice were injected serotonin, they scratched as much as the control mice after being exposed to itch-inducing compounds.

Chen’s team thinks it might be possible to hinder the communication between the serotonin and nerve cells in the spinal cord that specifically transmit itch. After conducting several more mice experiments, they discovered that the 5HT1A receptor was the means to stimulating the itch-specific GRPR neurons in the spinal cord. When the team blocked the 5HT1A receptor in mice, they scratched a lot less than the control mice.

The study’s findings are described in greater detail in the journal Neuron.