health
Now, researchers better understand why even a mildly annoying itch can set you into a cycle of itching and scratching if you give in.
A mosquito feeds on a technician at the Salt Lake City Mosquito Control District on July 26, 2023, in Salt Lake City. (AP Photo/Rick Baumer, File) AP
WASHINGTON (AP) — You’ve probably heard it since childhood: Don’t scratch an insect bite or rash, you’ll make it worse. But why is something that looks good bad?
There are many things that can cause itching, Sometimes serious illnesses. Whatever the cause, doctors have long warned that excessive scratching can cause damage Skin. Now, researchers better understand why even a mildly annoying itch can set you into a cycle of itching and scratching if you give in.
How did they find out? Partly by placing tiny “shame cones” on mice to reveal what’s going on At the cellular level When the itch is scratched – or left alone.
They also gained insight into why a good scratch, at least initially, brings a sigh of relief. After all, it’s not just humans and other mammals, but even fish. The commonality suggests there must be some evolutionary reason, and the mouse experience suggests there is a little protection from germs, but still not a reason for scratching.
Expect a more swollen and itchy spot if you can’t ignore the insect bite
Dr. Daniel Kaplan, a dermatologist at the University of Pittsburgh who studies immune reactions in the skin, was exploring a common type of itching called allergic contact dermatitis, caused by irritants like poison ivy or nickel in jewelry.
Kaplan’s research team applied a rash-causing irritant to the ears of mice. Normal mice were scratched and inflammatory immune cells rushed to the site, leading to increased swelling. The rash was much milder in mice bred with defective itch-sensing neurons. But was the difference really the scratch?
Normal mice that were put in collars like those veterinary “cones of shame,” so that they felt itchy but couldn’t scratch, gave the answer: They also had much less swelling and fewer inflammatory cells.
The evidence matches people’s everyday experiences that scratching can make things worse, Kaplan said.
If you ignore a mosquito bite, the itch will go away within five or 10 minutes for most people, he said. “But if you start scratching it, it will be your friend for a week,” and it becomes more itchy and inflamed.
The immune system’s first responders can help and harm
To understand what’s happening in the skin, Kaplan’s team took a deeper look at mast cells, among them Immune system First responders. When activated, they release compounds that can help fight germs or toxins — or, through a compound called histamine, trigger allergic reactions that cause itching.
Scientists have long known that allergens can activate mast cells. But other signals can also trigger mast cells, including pain. When we scratch, “we tend to scratch until the pain starts,” Kaplan noted.
Pain-sensing neurons release a chemical messenger called substance P. In findings published last year, Kaplan’s team reported that substance P can activate mast cells through a different molecular pathway than allergens do — a double whammy that explains why scratching increases the inflammation of rashes or bites.
So why is a simple scratch a good thing?
If we feel pain like touching a hot stove, we will learn never to do that again. However, a good recovery from scratch is, in evolutionary terms, positive feedback. Why?
One old theory is that it may help organisms get rid of parasites such as fleas or mites. But Kaplan was also intrigued by findings from other labs that mast cells can fight off a common type of skin bacteria called Staphylococcus aureus. So his team infected mice and then repeated the cone-of-shame itch experiment. Those who scratched certainly had lower levels of MRSA in their ears, perhaps due to additional inflammation or some other compound associated with the mast cells.
But that’s not enough of a positive side to change health advice.
“Ultimately, scratching is harmful,” Kaplan emphasized. “You have to avoid scratching,” he said, although he admitted that “it’s easier said than done.”
Here’s how to deal with a simple itch
What fights the itch depends on its cause, and better treatments are needed. Currently, antihistamines and some other medications used to treat urticaria can relieve some of the itching caused by mast cells. Pharmaceutical companies are trying other approaches called MRGPRX2 blockers that target the pathway that Kaplan’s team linked to scratching. Kaplan hopes that a better understanding of this pathway will eventually help skin conditions like chronic eczema.
For summer itch caused by insect bites, poison ivy and other types of contact dermatitis, dermatologists recommend using an anti-itch balm such as hydrocortisone cream, calamine lotion or oatmeal baths.
Another trick from Kaplan: Creams containing menthol can temporarily trick the skin into feeling cold instead of itchy, long enough that “if you don’t scratch, you’ll break the itch-scratch cycle.” “It’s like a cheat code.”
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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. AP is solely responsible for all content.