Scratching a mosquito bite may provide temporary relief, but why does it do so? Researchers have discovered that scratching activates an immune response that protects the skin against infections in mice. The study, published today in Science, sheds light on how scratching causes inflammation and explains why people often find the sensation satisfying.
In a bid to understand the purpose of scratching, scientists applied a synthetic allergen to mice’ ears, inducing an allergic contact dermatitis reaction. When control mice scratched their irritated ears, they developed swelling and increased neutrophil activity. However, mice wearing tiny Elizabethan collars or those with impaired itch-sensing neurons showed reduced inflammation.
Further investigation revealed that scratching triggers the release of substance P, a powerful nervous-system messenger that activates mast cells. These cells then recruited neutrophils to the scratched site, driving inflammation. The study’s findings indicate that mast cells can be triggered not only by allergens but also by scratching itself.
The researchers’ work has provided a molecular basis for understanding how scratching causes inflammation and may explain why people find the sensation so satisfying.
Source: https://www.nature.com/articles/d41586-025-00256-3