Scratching an itchy mosquito bite or rash may offer immediate relief, but it ultimately intensifies skin inflammation and prolongs the discomfort, according to research from the University of Pittsburgh. The findings, published in the journal Science, explain the biological mechanism behind why scratching exacerbates itching and inflammation.
Scientists investigating the itch-scratch-inflammation cycle applied an allergen to the ears of mice to induce a condition similar to eczema. They observed that scratching led to the activation of mast cells, which are key components of the body's immune response. These cells release histamine, a chemical responsible for itchiness, and substance P, a signaling molecule that further activates mast cells. This creates a feedback loop, known as the itch-scratch cycle, that amplifies inflammation and extends the duration of the itch.
Mice that were allowed to scratch freely exhibited greater inflammation compared to those prevented from scratching or genetically modified to lack itch-sensing neurons. The study suggests that while scratching can provide a temporary sensation of pleasure, this behavior likely evolved to offer a benefit such as defense against bacterial skin infections.
Researchers found that scratching reduced the levels of Staphylococcus aureus, a bacterium commonly associated with skin infections. However, they cautioned that the damage caused by scratching likely outweighs this potential benefit, especially in cases of chronic itching.
The American Academy of Dermatology recommends alternative methods for itch relief, such as using cold compresses or applying 1% hydrocortisone cream. These approaches can help soothe the skin without triggering the inflammatory cycle associated with scratching.
