Brains scans have revealed why scratching an itch can afford such intense pleasure even to the point of bleeding.

Researchers used imaging technology to see, for the first time, what happens within the brain when we scratch, and why the sensation gives so much pleasure even though it may damage the skin.

“Our study shows for the first time how scratching may relieve an itch. It’s important to understand the mechanism of relief so we can develop more effective treatments,” Dr. Gil Yosipovitch, a dermatologist from Wake Forest University Baptist Medical Centre, North Carolina, who led the research, said in the study.

The study recorded how the brains of 13 healthy patients responded to gentle scratching on the lower leg. They were monitored while they spent five minutes alternatively scratching for 30 seconds and resting for 30 seconds.

The researchers found that scratching reduced activity in the anterior cingulate cortex and the posterior cingulated cortex, areas linked with pain aversion and memory.

“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. We know scratching is pleasurable, but we haven’t known why,” Yosipovitch said.

The more intensely a person was scratched, the less activity they found in these areas of the brain.

“It’s possible that scratching may suppress the emotional components of itch and bring about relief. 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,” Yosipovitch said.

The study funded by the National Institutes of Health appears online in the Journal of Investigative Dermatology