Why scratching bug bites makes them worse, according to science

That satisfying scratch you give to an irritating bug bite or rash might feel good in the moment, but science explains why it's a bad idea. Doctors have long advised against excessive scratching, and new research is shedding light on the cellular mechanisms that explain why giving in to the urge can actually make the itch worse and prolong discomfort.

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But why would something that feels so good be bad?

Researchers studying allergic contact dermatitis, often caused by irritants like poison ivy or nickel, conducted experiments on mice. They found that mice equipped with Elizabethan collars, preventing them from scratching, experienced significantly less swelling and inflammation compared to those that could scratch their induced rashes. This suggests that the physical act of scratching itself contributes to the inflammatory response.

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Normal mice put into collars like those veterinary “cones of shame” so they itched but couldn’t scratch gave the answer: They, too, had much less swelling and fewer inflammatory cells.

The relief from scratching is temporary because the sensation triggers a complex immune response. When we scratch, especially to the point of pain, we activate pain-sensing nerve cells. These cells release a chemical messenger called substance P, which can activate mast cells. Mast cells are key players in the immune system; they release compounds like histamine, which are responsible for triggering itchy allergic reactions.

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Ignore a mosquito bite and the itch is “gone in five or 10 minutes for most people,” he said. “But if you start scratching it, it’s your friend for a week,” getting itchier and more inflamed.

While scratching might offer a brief respite, it ultimately perpetuates an itch-scratch cycle. Ignoring a minor itch, like a mosquito bite, often allows it to subside naturally within minutes. However, scratching can transform a fleeting annoyance into a week-long problem, characterized by increased itchiness and inflammation. Understanding these cellular processes reinforces the common advice: resist the urge to scratch.

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And when we scratch, “we tend to scratch until it starts to hurt,” Kaplan noted.