Scratching also has advantages

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If something itches, don’t scratch it because it will itch even more: small children are taught this. However, scratching has a double effect, as new research shows: On the one hand, it exacerbates skin inflammation, and on the other, it can strengthen the immune system.

From an evolutionary perspective, it’s actually a paradox: if scratching is so harmful, why does it feel so good? “It must also offer some kind of benefit,” says Daniel Kaplan, a dermatologist at the University of Pittsburgh and lead author of a study that has just been published in the journal Science. “It helps to resolve the paradox.”

Further damage to the skin
Kaplan’s team conducted experiments with two types of mice to investigate the advantages and disadvantages of the “itch-scratch cycle”. Some did not feel itchy because they lacked the corresponding nerve cells, while the others were “normal” mice.

Both ears were treated with itch-inducing allergens.

When normal mice were allowed to scratch, their ears became inflamed, swollen and filled with certain immune cells, the neutrophils. In contrast, inflammation in normal mice that could not scratch was much milder. These mice wore tiny “Elizabethan collars” – cone-like collars similar to those worn by dogs and cats after a vet visit, preventing scratching.

The same applied to animals that lacked itch-sensitive nerve cells. This experiment confirmed that scratching further damages the skin.
But also fewer bacteria
The research team discovered that scratching activates pain-sensitive nerve cells that release a certain substance (“SP”). This, in turn, stimulates certain cells to increase inflammation. Scratching, therefore, exacerbates problems such as dermatitis.

At the same time, however, it can support the immune system, as further experiments with mice have shown. Scratching rodents had fewer bacteria on their skin, such as Staphylococcus aureus, the most common bacterium in skin infections. Scratching can, therefore, protect against bacterial infections.

The disadvantages outweigh the benefits
“Our results suggest that it can also be beneficial,” says Kaplan in a press release from the University of Pittsburgh. However, this is not a carte blanche for scratching: the itching is intensified, and the disadvantages outweigh the benefits, especially in chronic cases.

“Apart from defining a previously unknown ‘itch-scratch cycle’, the results of the study could provide a basis for discoveries that help people with chronic itching,” comments Aaron Ver Heul, an allergist at the University of Washington, in an accompanying article in ‘Science’. Work is already underway on appropriate therapies for dermatitis and rosacea.