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Asked by alfmoousk on 14 Apr 2025.
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Luke Humphrey answered on 14 Apr 2025:
Great question! I don’t know much about this, but on a basic level the reason we itch is probably for sweeping away dangerous things like venomous insects. If you feel something on your skin, you get an urge to scratch it, which likely removes the insect before it can do more damage, and you feel some relief as part of the body’s reward system.
But it’s interesting how we can itch from many other things as well. And a lot of the time, scratching an itch can actually do more damage if you tear the skin or disrupt the healing process.
I’ve actually recently been to the vets because my dog had some skin infections. It turns out he has allergies which were making him itchy, which caused him to scratch until his skin and fur were damaged, which led to the infection. Skin & fur act as a barrier to infection; so it’s very interesting that what should be a protective instinct to scratch away dangerous things can turn into a danger in itself.
His recovery is going very well (just so you’re not worrying). One of the medications he’s on now is specifically to reduce the itchiness and it’s been very effective. He stopped scratching within hours and his injuries healed in a few days!
I’d love to hear more from any biologists on here who might know more about why we itch even when it can be harmful to us.
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Charlotte Slade answered on 1 Jul 2025:
That is a brilliant question that every single person has wondered about!
Now, my world is usually physics—the science of forces, energy, and the building blocks of the universe. The itch is the territory of biology, but the science behind it is so cool that I can’t resist explaining it.
Think of your skin as a really smart security system for your body. An itch is basically the alarm bell.
When something irritates your skin—like a mosquito bite, a piece of scratchy wool, or just some dry skin—special cells in that spot get triggered. They release a chemical messenger called histamine.
That messenger’s job is to run to your nerves and say, “Alert! Alert! Something is happening here that shouldn’t be!”
That nerve signal zips all the way up to your brain. Your brain gets the message and does the only thing it knows how to do to get your attention: it makes you feel that maddening, distracting, gotta-scratch-it-now feeling.
And why does scratching feel so good for a moment? When you scratch, you’re creating a different, mild pain signal. That signal travels along a faster nerve “highway” to your brain, and it basically shouts over the itch signal, giving you some relief. It also helps to physically remove whatever was causing the problem in the first place.
So even though it can drive you crazy, an itch is just your body’s clever, built-in alarm system telling you to check on something. It’s a brilliant piece of biology
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