Scratching that bug bite might feel good at first but science explains
why it's a bad idea
[June 29, 2026]
By LAURAN NEERGAARD
WASHINGTON (AP) — You’ve likely heard it since childhood: Don’t scratch
that bug bite or rash, you’ll make it worse. But why would something
that feels so good be bad?
A lot of things can cause itchiness, sometimes serious diseases.
Whatever the cause, doctors have long warned that scratching too much
can damage the skin. Now researchers better understand why even a mildly
annoying itch could put you on an itch-and-scratch cycle if you give in.
How did they find out? In part by putting tiny “cones of shame” onto
mice to uncover what happens on a cellular level when an itch gets
scratched — or left alone.
They also gained insight into why a good scratch at least at first
brings a sigh of relief. After all, not just people and other mammals
scratch, even fish do. The commonality suggests there must be some
evolutionary reason and the mouse experiment hints at a little germ
protection — but still not a reason to scratch.
Expect a more swollen, itchier spot if you can't ignore that bug bite
Dr. Daniel Kaplan, a University of Pittsburgh dermatologist whose lab
studies immune reactions in skin, was exploring a run-of-the-mill type
of itch called allergic contact dermatitis, caused by irritants such as
poison ivy or nickel in jewelry.
Kaplan's research team put a rash-inducing irritant on the ears of mice.
Normal mice scratched and inflammatory immune cells rushed to the site,
increasing swelling. The rash was much milder in mice bred with
defective itch-sensing nerve cells. But was the difference really the
scratching?
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.
Kaplan said that evidence matches people’s everyday experiences that
scratching really can make things worse.
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.
The immune system’s first responders can help — and hurt
To understand what was happening in the skin, Kaplan’s team took a
deeper look at mast cells, among the immune system’s first responders.
When called into action, they release compounds that can help fight
germs or toxins — or, through a compound called histamine, trigger itchy
allergic reactions.
Scientists have long known that allergens can activate mast cells. But
other signals can summon mast cells, too, including pain. And when we
scratch, “we tend to scratch until it starts to hurt,” Kaplan noted.
Pain-sensing nerve cells 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
further inflames itchy rashes or bites.
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A mosquito feeds on a technician at the Salt Lake City Mosquito
Abatement District on July 26, 2023, in Salt Lake City. (AP
Photo/Rick Bowmer, File)
 Then why does a little scratching
feel good?
If we experience pain like touching a hot stove, we’ll learn not to
do that again. Yet relief from a good scratch, in evolutionary
terms, is positive feedback. Why?
One long-held theory is that it may help creatures slough off
parasites like fleas or mites. But Kaplan also was intrigued by
other labs’ findings that mast cells could fend off a common type of
skin bacteria called Staphylococcus aureus. So his team infected
mice and then repeated the cone-of-shame itch experiment. Sure
enough, those that scratched had lower levels of that germ on their
ears, maybe because of the extra inflammation or some other mast
cell-related compound.
But that's not enough of an upside to change the health advice.
“Ultimately, scratching is deleterious,” Kaplan stressed. “You
should avoid scratching,” he said, although acknowledging that it’s
“easier said than done.”
Here’s how to handle a minor itch
What fights an itch depends on its cause and there's a need for
better treatments. For now, antihistamines and certain other drugs
for hives can tamp down some itchiness triggered by mast cells. Drug
companies are experimenting with other approaches called MRGPRX2
blockers that target the pathway Kaplan’s team linked to scratching.
Kaplan hopes better understanding of that pathway eventually could
help skin diseases such as chronic eczema.
For the summer itchiness of bug bites, poison ivy and other types of
contact dermatitis, dermatologists recommend anti-itch balms such as
hydrocortisone cream, calamine lotion or oatmeal baths.
Another trick from Kaplan: Menthol-containing creams can temporarily
fool the skin into sensing cold instead of itch, just long enough
that “if you don’t scratch, then you break that itch-scratch cycle,”
he said. “It’s like a cheat code.”
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