Many skin conditions can make you itch including insect bites, allergic reactions and exposure to various chemicals. While scratching an itch may seem to provide temporary relief, scientists at the Washington University School of Medicine in St. Louis have identified the best way, long-term, to cope. And it is not by scratching.
When you scratch an itch, the immediate itch reduction you experience is caused by the small pain you create when scratching. The mild pain stimulates spinal cord nerve cells to convey pain messages to the brain instead of itchy signals.
But that mild pain quickly leads to added secretion of serotonin, a neurotransmitter which dampens pain but stimulates extra itching.
“The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain,” says researcher Zhou-Feng Chen. “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.”Despite the intricacies of the reactions that lead to more itchiness, the best way to deal with an itch and lower its intensity is pretty simple: Don’t scratch it.
The problem arises because serotonin interacts with nerve units in the spinal cord called GRPR neurons which are designed to pass on itch signals from the skin to the brain. The GRPR neurons contain what are called 5HT1A receptors that make them sensitive to serontonin.
“We always have wondered why this vicious itch-pain cycle occurs,” says Chen who directs Washington University’s Center for the Study of Itch. “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.”