The Daily Populous Sunday February 2nd, 2025 day edition
Authored by nature.com and submitted by broc944

Itchy-scratchy: experiments show that there are benefits to scratching ― although it can also aggravate skin disease. Credit: Getty

Scratching a mosquito bite can offer a moment of bliss, and now scientists know why: scratching activates an immune response that helps to protect the skin against harmful infections, at least in mice.

The findings could also explain why people find a good scratch satisfying. The study1 was published today in Science.

“The exciting thing about this study is that there’s now a molecular basis” for how scratching causes inflammation, says Aaron Ver Heul, an immunologist at Washington University School of Medicine in St. Louis, Missouri, who was not involved in the study. The work, he adds, is “rigorous” and “really well done”.

Almost all animals scratch, even though scratching too much can damage the skin. The classic explanation for scratching is that it removes parasites and irritants. “But we’ve always thought there might be other reasons,” says Ver Heul. After all, some parasites, such as mosquitoes, are long gone by the time itching starts.

To get to the root of the matter, skin immunologist Dan Kaplan at the University of Pittsburgh in Pennsylvania and his colleagues painted a synthetic allergen onto the ears of mice. This induced a form of skin inflammation called allergic contact dermatitis, which is caused by contact with an allergen such as the oil in poison ivy. When control mice scratched, their ears swelled up and became full of neutrophils, a type of immune cell.

But mice that wore tiny Elizabethan collars — the rodent version of the ‘cone of shame’ that dogs sometimes need to wear after surgery — couldn’t scratch their irritated ears. These animals’ ears showed less swelling and contained fewer neutrophils than the ears of control mice did. Bioengineered mice that were lacking an itch-sensing neuron exhibited a similarly muted reaction. The experiment showed that the act of scratching itself worsens inflammation.

To learn more about what happens after scratching, the scientists studied ordinary mice that were allowed to scratch their itchy ears. They noticed that at scratched sites, pain-sensing neurons released a potent nervous-system messenger called substance P.

Substance P activated key white blood cells called mast cells, which are central to triggering allergy symptoms. The mast cells recruited neutrophils to the scratched site, driving inflammation.

Researchers already knew that mast cells can be turned on directly by allergens. The authors’ work revealed that mast cells can also be turned on indirectly, by scratching and the sequence of steps it initiates.

rodneedermeyer on February 1st, 2025 at 23:57 UTC »

Who here discovered at least three separate itches upon reading this headline?

gammaxgoblin on February 1st, 2025 at 23:27 UTC »

The article did not provide me with a sense of direction. Yes it feels good and it increases inflammation. Inflammation good? sometimes, in the right amount. Inflammation bad? Sometimes, if too much. JUST TELL ME TO SCRATCH OR NOT!!!

barnabasthedog on February 1st, 2025 at 23:24 UTC »

Eczema joins the chat.