Study Finds Scratching Intensifies Eczema Inflammation by Activating Mast Cells
Research on mice shows that scratching triggers mast cell activation and histamine release, worsening skin inflammation and extending the itch-scratch cycle, while limiting scratching reduces these effects.
University of Pittsburgh researchers discovered that scratching an irritated skin area can amplify inflammation in eczema-like conditions. In experiments, mice exposed to an allergen that induces allergic-contact dermatitis were allowed either to scratch freely or were prevented from doing so with a collar. The freely scratching group showed higher levels of substance P, which activated mast cells and released histamine, leading to greater swelling and a prolonged itch-scratch loop. Mice that could not scratch or that lacked itch-sensing neurons exhibited less inflammation.
The study also examined the impact of scratching on skin bacteria. While scratching reduced the presence of Staphylococcus aureus, the investigators noted that the overall damage to the skin from chronic scratching likely outweighs any antimicrobial benefit. "The damage that scratching does to the skin probably outweighs this benefit when itching is chronic," said Daniel H. Kaplan, professor of dermatology and immunology at the University of Pittsburgh.
Kaplan added that the pleasurable sensation of scratching, which evolved millions of years ago, may have once served a defensive role against pathogens, but in chronic conditions it becomes detrimental. The findings were published in the journal Science and align with dermatology guidelines that recommend cold compresses and low-strength hydrocortisone creams to alleviate itching.