New research has found that scratching triggers an immune response that helps protect the skin from harmful infections. This opens up new treatment options for patients with chronic itch.
Scratching an itch may help fight bacteria, new research suggests - Illustration created by AI
The pleasurable sensation of scratching a mosquito bite is something everyone has experienced. Now scientists have figured out why: scratching triggers an immune response that helps protect the skin from harmful infections, at least in mice.
Scratching is a seemingly simple behavior, but it occurs in most animals, although excessive scratching can cause skin damage. According to the traditional explanation, animals scratch to remove parasites and irritants. However, this does not explain why we still itch and want to scratch even when the itch-causing agent, such as a mosquito, has long since disappeared.
To further understand this mechanism, Dr. Dan Kaplan's research team at the University of Pittsburgh conducted experiments on mice.
They applied a synthetic allergen to the ears of mice, causing a form of allergic contact dermatitis similar to that caused by exposure to castor oil. The results showed that when the mice were allowed to scratch freely, their ears swelled and filled with neutrophils – an important type of immune cell.
In contrast, mice wearing small collars were unable to scratch their ears and had significantly fewer inflammatory symptoms.
Similarly, mice genetically engineered to lack itch-sensing neurons also showed a weaker inflammatory response, suggesting that scratching itself exacerbates inflammation.
Digging deeper into the mechanism, scientists discovered that at the scratching site, pain-sensing nerves release substance P - a powerful neurotransmitter. This substance P activates mast cells, a type of white blood cell that plays a key role in triggering allergic symptoms. Mast cells then attract neutrophils to the scratching site, causing an inflammatory response.
It has been known for some time that mast cells can be directly activated by allergens. The new study shows that they can also be activated indirectly, through scratching and the chain reaction that follows. Neutrophil-induced inflammation was significantly increased when mice scratched and activated both pathways.
Notably, the day after exposure to the allergen, mice that were allowed to scratch had less dangerous Staphylococcus aureus bacteria on their skin than either the group that couldn’t scratch or the group that had been genetically engineered to not feel itchy. This finding suggests that scratching has antibacterial benefits, explaining why we find it satisfying to scratch an itch.
However, Dr. Kaplan cautions that the study only focused on acute itch. With chronic itch caused by conditions like eczema or diabetes, constant scratching can damage the skin and allow S. aureus bacteria to thrive.
Hope for Chronic Itch Sufferers
According to scientists, understanding the mechanism of scratching can open up new treatment directions for people with chronic itching.
Research suggests that the body has one set of nerves that transmit itch signals and another set that responds to scratching by increasing inflammation. If scientists can separate these two sets, they could block each one. This could be helpful when the itch is uncomfortable but the inflammation that comes with it is beneficial to the body's immune response.
"There's a vicious cycle of 'itching and scratching' that's hard to break," said Aaron Ver Heul, an immunologist not involved in the study. "Identifying this neural circuit could lead to better treatments to interrupt that vicious cycle."
Source: https://tuoitre.vn/phat-hien-loi-ich-bat-ngo-cua-gai-ngua-20250201131418929.htm
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