Four-legged animals do it. Two-legged animals do it. Now, new research provides insight into why scratching an itch feels so good.
"Our study shows for the first time how scratching may relieve itch," said lead researcher and dermatologist Gil Yosipovitch, M.D., of Wake Forest University Baptist Medical Center. "It's important to understand the mechanism of relief so we can develop more effective treatments. For some people, itch is a chronic condition that affects overall health."
The study tested 13 people, using MRI technology to highlight areas of the brain activated during an activity. Participants were scratched on the lower leg with a small brush. The scratching went on intermittently — 30 seconds on and 30 seconds off — for five minutes.
"To our surprise, we found that areas of the brain associated with unpleasant or aversive emotions and memories became significantly less active during the scratching," said Yosipovitch. "We know scratching is pleasurable, but we haven't known why. It's possible that scratching may suppress the emotional components of itch and bring about its relief."
The reduced brain activity occurred in the ACC, the anterior cingulate cortex, an area associated with aversion to unpleasant sensory experiences, and the posterior cingulate cortex, which is associated with memory.
"This is the first real scientific evidence showing that itch may be inhibited by scratching," he said. "Of course, scratching is not recommended because it can damage the skin. But understanding how the process works could lead to new treatments. For example, drugs that deactivate this part of the brain might be effective."
The imaging studies also showed that some areas of the brain were made more active by the scratching, including the secondary somatosensory cortex, a sensory area involved in pain, and the prefrontal cortex, which is associated with compulsive behavior.
"This could explain the compulsion to continue scratching," said Yosipovitch.
Understanding more about chronic itch is important, Yosipovitch said, noting that more than 30 million Americans suffer from eczema and that almost half of kidney dialysis patients are bothered by severe itching.
This study is reported online in the Journal of Investigative Dermatology and will appear in a future print issue.