Mouse Experiments Link Scratching to Increased Skin Swelling

A University of Pittsburgh study found that scratching an irritated patch of skin recruits inflammatory immune cells and increases swelling. nypost.com reported the results from experiments on mice with allergic contact dermatitis. Dr.

Daniel Kaplan’s team applied a rash-inducing irritant to the ears of normal mice. The animals scratched the site, after which inflammatory cells accumulated and swelling rose. Mice engineered with defective itch-sensing nerve cells developed noticeably milder rashes under the same conditions.

To isolate the effect of scratching itself, researchers fitted normal mice with small collars that prevented them from reaching the irritated skin. These animals also showed reduced swelling and fewer inflammatory cells compared with mice allowed to scratch. Kaplan stated that the mouse data align with common human experience.

“Ignore a mosquito bite and the itch is gone in five or 10 minutes for most people,” he said. “But if you start scratching it, it’s your friend for a week,” he added, noting greater itchiness and inflammation. The experiments used tiny cones similar to veterinary “cones of shame” to keep the mice from scratching while researchers observed cellular changes.

Kaplan’s lab studies immune reactions in skin and focused on everyday irritants such as poison ivy or nickel.