Why does itching in the body move when we scratch it

Getting a back scratch is one of the most satisfying feelings ever. At least until you can’t quite hit the right spot because it’s a little to the left, no, to the right, wait, no. Then it’s just frustrating because it feels like your itch is actually moving around your body. And it's all thanks to some tricks of your nerves.

An itch is a not-so-delightful sensation that, as soon as you feel it, you feel like you need to scratch, and it can be caused by all sorts of things, like skin irritation, overactive nerves, or even something systemic like kidney disease. And that need to scratch distinguishes itchiness from other unpleasant sensations like pain, but the two feelings have a lot more in common than meets the eye.

Like, these two sensations, itchiness and pain, send messages through the same kinds of neurons to a common destination: the spinal cord. Which threw scientists for a loop, making them think that itchiness was actually just a subset of pain. Research suggests that different groups of neurons are responsible for itch, which means that itchiness and pain are separate sensations.

But they still interact with each other. Like, processing pain might actually be why scratching an itch feels so good. See, scratching kind of hurts, because you’re lightly damaging the skin. And those pain signals get sent to the spinal cord, overriding the itchiness signals. Your brain doesn’t notice the itchiness; it detects mostly pain.

So, it releases a chemical messenger, serotonin, to help ease that pain. Every time you scratch, your brain is getting bathed in serotonin,which makes it feel pleasurable. But once you’ve scratched, it might feel like the itchiness moved a to the left.

Scientists don’t know exactly why that is, but there are a couple possibilities.One has to do with the distribution of pain receptors in the skin. There are more receptors in the skin than nerve fibers leading to the spinal cord, so many receptors have to send their signals to one nerve.

And by the time the itch signal gets to the brain, it might not be able to tell exactly which receptors it started in, just a general area.So as you scratch, it may feel like the itchiness is moving because your brain sort of guesses where it started and sometimes guesses wrong.

That may also be related to why an itch often comes back stronger once you stop scratching it. The serotonin that makes itching feel good spreads from the brain back down to the spinal cord, where it’s supposed to help reduce pain. But serotonin also stimulates the nerves that carry itchiness information.

And when those nerves are extra stimulated, the itch might feel even itchier than before you scratched. But because of that difference in the number of receptors and the number of nerves, that new, extra-intense itchiness could be perceived as coming from spots nearby the original itch. So, your scratching kicks off a signaling cascade that ends in feeling like the itchiness is moving.

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