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

Everybody knows how difficult it can be resist scratching away, usually surreptitiously for fear of giving the impression of having lice or fleas, but the reasons have remained a mystery.

Images of the brain’s responses to scratching have revealed that the action suppresses activity in regions of the brain associated with unpleasant memories and emotions.

Researchers made the discovery during experiments in which 13 volunteers were asked to scratch their legs with a small brush. Magnetic resonance imaging (MRI) was used to monitor the subjects’ brains while they spent five minutes alternately scratching for 30 seconds and resting for 30 seconds.

“Our study shows for the first time how scratching may relieve itch,” said Dr Gil Yosipovitch, a dematologist at Wake Forest University Baptist Medical Center in the United States.

He added: “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.”

The findings of the research were published online in the Journal of Investigative Dermatology.

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