Researchers explain why scratching insect bites worsens inflammation
A study using mice shows that scratching an itch triggers immune responses that increase swelling and can prolong discomfort, confirming medical advice to avoid scratching.
Scientists have clarified the biological reasons why scratching an itch, such as a bug bite, can make the irritation last longer. In experiments at the University of Pittsburgh, researchers applied an irritant to the ears of mice and observed that animals allowed to scratch showed greater swelling and a higher influx of inflammatory immune cells than those prevented from scratching with protective collars.
"If you ignore a mosquito bite, the itch is gone in five or ten minutes for most people. But if you start scratching it, it can last a week and become more inflamed," said Dr. Daniel Kaplan, a dermatologist who led the study.
The team focused on mast cells, which release histamine and other compounds that trigger itching. They found that the pain-related neurotransmitter substance P, released during scratching, also activates mast cells through a separate pathway, amplifying the inflammatory response.
Additional tests showed that mice that scratched had lower levels of Staphylococcus aureus bacteria on their skin, suggesting a possible short-term antimicrobial benefit, but the researchers concluded that the overall effect of scratching remains detrimental.
Kaplan recommends avoiding scratching and using anti-itch treatments such as hydrocortisone cream, calamine lotion, oatmeal baths, or menthol-based products that temporarily mask the itch sensation. Ongoing research is exploring drugs that block the newly identified mast-cell pathway, which could lead to better therapies for chronic skin conditions.