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Why Do We Itch?

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Channel: BrainStuff - HowStuffWorks
Categories: Biology   |   Society / Culture   |   Environmental   |   Science   |   Social Science  
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Virtually everyone has experienced an itch at one time or another – but what is an itch exactly? What causes it, and why can having one be such a maddening experience?

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Hey there. I'm Josh Clark, and this is BrainStuff. And this is the BrainStuff where I talk to you about itching.

Just fair warning here: you are going to itch. Because I am a puppet master and you are my puppet. Just FYI.

So let's talk about skin. It's your birthday suit! And skin allows us to experience that ever so important sensation touch. Touch, in and of itself, is a very complex thing. It's multifaceted. And one of those facets - one of the chief facets among all touch - is the itch.

For a while, people thought that an itch was just a low level type of pain. And it makes a lot of sense. Because itches and pain (and actually the sensation of heat) all follow the same neural pathways from the skin to the brain. But a recent closer examination of your skin has found that your itch triggers a specific kind of receptor, called pruriceptors. Which is tough to say, but actually, it's a pretty legitimate term because another word for itch (the clinical term) is "pruritus."

Which is why everybody just calls it itch.

So these special receptors (pruriceptors) are attuned to just the most minute sense of touch. They're triggered by something like the ever-so-gentle pressure of a fly's legs. And, even closer examination of itching has found that these pruriceptors use a specialized neurotransmitter called MPPB to send the itch signal from the skin to the brain.

So, it turns out that itching is not pain. It's its own thing. A good analogy is that itches and pain might follow the same highway from the skin to the brain, but they start from slightly different points of origin, and an itch uses a different kind of car.

So science has a better handle on itches than it did before, but they're still a big mystery. Why should scratching an itch bring any sort of relief?

Well, itching appears to be a built-in warning system for us to say that there's something small but potentially dangerous that's just alighted on our skin. Right?

When we scratch whatever's causing that itch, the prevailing theory, is that we activate more skin cells than just the pruriceptors. Which means that the pruriceptors' itch signal is either drowned out by these other signals or potentially turned off somehow.

And that makes a lot of sense, because when you scratch an itch, your fingernail is exerting enough pressure, and is big enough, that it can destroy or get rid of whatever was causing the itch in the first place.


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