Study explains why scratching bug bites can worsen inflammation
Research using mice shows that scratching an itch increases swelling and immune cell activity, confirming medical advice to avoid scratching despite temporary relief.
Researchers at the University of Pittsburgh have clarified the biological basis for the long-standing warning against scratching itchy skin. In experiments, mice exposed to an irritant on their ears developed typical swelling and attracted inflammatory immune cells when they were allowed to scratch. By fitting the animals with protective collars that prevented scratching, the scientists observed markedly reduced swelling and fewer immune cells at the site.
Dr. Daniel Kaplan, a dermatologist who leads the study, said the findings mirror everyday experience: “Ignore a mosquito bite and the itch is gone in five or ten minutes for most people. But if you start scratching it, it’s your friend for a week,” indicating that scratching prolongs and intensifies the reaction.
Further analysis focused on mast cells, which release histamine and other compounds that can trigger itching. The team found that the pain-related neurotransmitter substance P, released during scratching, also activates mast cells through a separate pathway, compounding inflammation.
While a brief scratch can feel relieving, the researchers noted that it may have evolved to help remove parasites. In a separate test, mice that scratched after being infected with Staphylococcus aureus showed lower bacterial levels, possibly due to heightened inflammatory responses. Nonetheless, Dr. Kaplan emphasized that “ultimately, scratching is deleterious. You should avoid scratching,” even though it can be difficult.
For mild itch relief, dermatologists continue to recommend antihistamines, hydrocortisone cream, calamine lotion, oatmeal baths, or menthol-based products that create a cooling sensation and help break the itch-scratch cycle.