Mouse Study Finds Scratching an Itch Increases Swelling but Reduces Bacteria on Infected Skin

University of Pittsburgh researchers found that scratching an itch activates mast cells through a pain-related pathway and increases swelling at the site of irritation. In experiments, normal mice developed pronounced rashes after an irritant was applied to their ears, while mice prevented from scratching by veterinary collars showed markedly less swelling and fewer inflammatory cells. Dr.

Daniel Kaplan’s team also tested mice with defective itch-sensing nerve cells. Those animals experienced milder reactions, confirming that the act of scratching itself drives the amplified response. The same pattern held when the researchers repeated the collar experiment after infecting mice with Staphylococcus aureus; animals allowed to scratch cleared more of the bacteria from their ears.

Kaplan said the results align with everyday experience. “Ignore a mosquito bite and the itch is gone in five or 10 minutes for most people,” he said. ” Pain-sensing nerves release substance P during scratching, which activates mast cells through a route distinct from allergens, the team reported last year.

Kaplan concluded that scratching remains harmful overall. “scratching is deleterious,” he said. ” Current treatments include antihistamines for mast-cell-driven itch and topical options such as hydrocortisone cream, calamine lotion, or oatmeal baths.

Drug companies are testing MRGPRX2 blockers aimed at the scratching-linked pathway, and Kaplan noted that menthol creams can briefly substitute a cold sensation for itch to interrupt the cycle.