Scratching Bug Bites Worsens Inflammation, Research Suggests

Scratching an itchy mosquito bite or rash may provide momentary relief, but it ultimately exacerbates inflammation and prolongs the discomfort, according to research from the University of Pittsburgh. The study investigated the long-standing question of why scratching, an instinctive response to skin irritants, intensifies swelling and itching.

Researchers induced an allergic-contact dermatitis, an eczema-like condition, in mice by applying an allergen to their ears. Some mice were genetically modified to lack itch-sensing neurons, while others were allowed to scratch freely and some were prevented from scratching using collars. The study found that scratching activates mast cells, which are part of the body's immune defense system. These cells release histamine and other inflammatory chemicals that cause itchiness.

In mice that scratched freely, the signaling molecule substance P was released, activating more mast cells. This led to increased inflammation and a more persistent itch-scratch cycle. Conversely, mice that were prevented from scratching or lacked itch-sensing neurons experienced reduced inflammation.

While scratching activates mast cells, which can aid in protecting against bacteria and pathogens, the researchers noted that the damage caused by scratching, especially in cases of chronic itching, likely outweighs this benefit. The study's findings, published in the journal Science, suggest that while scratching might offer a short-term defense against bacterial skin infections by reducing bacteria like Staphylococcus aureus, it primarily contributes to a cycle of prolonged inflammation.

The American Academy of Dermatology suggests that cold compresses and 1% hydrocortisone cream can help alleviate itching without the detrimental effects of scratching.