Researchers from the Washington University School of Medicine in St. Louis say that scratching may cause the itching to intensify.
Pain signals cause the brain to trigger a release of serotonin. Scratching can cause minor pain, which may trigger the release of serotonin, causing the itch to get worse.
Serotonin is released by the brain to help the body control pain. As the serotonin spreads through the body and into the spinal cord, the chemical can move from pain-sensing neurons to the nerve cells that influence itch intensity.
For the study, scientists bred certain mice that lacked the genes to make serotonin. The mice were injected with a chemical that causes the skin to itch. The mice didn’t scratch as much as normal mice. The genetically-modified mice were then injected with serotonin and began to scratch as much as the normal mice.
Scientists also discovered that it was the receptor known as 5HT1A that was responsible for activating the GRPR neurons, which are itch-specific neurons. Scientists have noticed that blocking the 5HT1A made the mice itch less.