Here’s why your July 4 bug bites just keep getting itchier after scratching them

Piglet scratching itself
The cutest piglet ever relieves an itch against a wooden plank. Flickr/Eric Kilby

If you are still itchy from your July 4th BBQ bug bites, you only have yourself to blame.

We’ve all learned the hard way that scratching an itchy bug bite makes it worse — and now scientists have figured out why.

Researchers used to believe that itch was simply a weak form of pain. But in 2009, scientists at Washington University in St. Louis found itch-specific nerve cells in the brains of mice — indicating they are different. While pain and itch are processed separately, they are closely related and travel on the same pathways to the brain, so an itch can sometimes feel painful.

We still don’t understand how the brain discriminates between pain and itch. But we do know that, at least for a moment, scratching an itch causes a short sensation of pain, which for a second, masks the itch.

It all has to do with a little feel-good chemical in the brain called serotonin. Serotonin is involved in many roles in the body. It helps to modulate everything from appetite, mood, the desire for sex, and pain.

When the brain recognises pain from the scratching, it tries to mask it with serotonin.

But then the itch comes back with a vengeance.

Scientists found that the serotonin then turns on nerve cells that cause itchiness again. This is because the nerve cells that cause itch have two receptors that sit closely together: one that induces itch and another that promotes pain relief. When serotonin arrives, it indirectly sets off both pathways.

This ends up being a vicious cycle. When you feel an itch, you scratch it, which releases serotonin which inevitably makes you feel itchy again. And on and on.

While these itch-specific neurons haven’t been found in humans specifically — they are present in our relatives the macaques — it’s still safe to say that scratching an itch will only come to bite you later.

Our friends at Chemical & Engineering News put together a short explainer on the science of itching and why that sweet, sweet relief of scratching only makes it worse.

What the video doesn’t answer, though, is why watching a video about itching makes you itch. Maybe fodder for a next segment?

Check it out:

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