Scratching an Itch Is Bad. And Also Good.

If you’ve got an itch somewhere on your body, it’s probably best not to scratch it. New research suggests that scratching an itch, while satisfying in the moment thanks to the release of the “feel-good hormone” serotonin, actually creates more inflammation. But it’s not all bad. Scratching an itch also provides you with a little bit of protection from bacterial skin infections.

A research team from the University of Pittsburgh studied mice with allergic contact dermatitis, a condition that presents itself as a bunch of itchy rashes. The results, published in the academic journal Science, suggested that when mice scratched their itches, the problem areas became inflamed, and immune cells called neutrophils swooped in to repair the damage.

Another set of mice was not allowed to scratch. Now, you might be wondering how you get a mouse to not scratch an itch. It’s quite simple: you know those plastic cones you put around the dog’s head so they don’t bite a rash or incisions cars? The researchers use tiny versions of those around the mouse’s head. They must’ve been adorable.

The results were clear: the mice that could not scratch had less inflammation, meaning that scratching aggravates the itch and your skin, only making matters worse. Scratching activates a pain-sensing neuron that releases a chemical with the ominously unspecific name “substance P.”

It triggers a response from an immune cell responsible for inflammation and itchiness. In the case of allergic dermatitis, the cells are also activated by allergens, creating a big feedback loop that only makes the itching worse.

You’ve met substance P, an evil little scamp that makes the relief you feel from scratching an itch only temporary. Now meet Staphylococcus aureus, a bacteria that causes skin infections. You might know it better as a Staph infection. It can cause boils, blisters, and general redness anywhere on your body.

The researchers found that scratching actually helps reduce the amount of Staphylococcus aureus on your skin.

“The finding that scratching improves defense against Staphylococcus aureus suggests that it could be beneficial in some contexts,” senior study author Dr. Daniel Kaplan said. “But the damage that scratching does to the skin probably outweighs this benefit when itching is chronic.”