(Intro)

Itching. Just thinking about it is making me kinda itchy. An itch can be caused by all kinds of things. The usual culprits are things like bug bites, poison ivy, or strands of hair brushing against your skin. But it's also brought on by skin conditions like eczema or psoriasis as well as seemingly unrelated things like brain tumors, diabetes, and chemotherapy. With such a wide range of causes the itch seems to be kind of mysterious. And it is.

But in a 2013 study published in the journal Science, two researchers from the National Institutes of Health discovered the physiology of how itching works, which may eventually help chronic itchers find relief. Scientists used to think that an itch was basically a low-level pain signal, meaning that one kind of nerve cell detected both itching and pain. But the study found that itching is actually linked to a set of special neurons that produce a neuropeptide called NPPB.

The scientists genetically engineered mice so that they wouldn't produce NPPB, then exposed the mice to chemicals known to produce itching. These mice could still feel their bodies, heat, pain, and touch, but they didn't scratch. No NPPB, no itch. That's good news for people who want to stop itching, because the more we understand about how itching works, the closer we can get to be able to control it.

Unfortunately, it's not as simple as just blocking this neuropeptide, because NPPB has another job, too. It's released by the heart to regulate the amount of sodium released by the kidneys, which helps control blood pressure. But for most people, blocking itching wouldn't be a good idea anyway. The itch gets a bad rap, but it's a useful evolutionary development. Scratching an itchy spot could remove a pesky bug, a dangerous plant, or some kind of other irritant before they do damage to your body.

With all this talk of itching, you might be starting to feel pretty itchy by now. I know I am. Just thinking about itches can make you feel like spiders are crawling all over you. Researchers gave a lecture about itching to an unsuspecting crowd to study their response, and the audience got to scratching with both verbal and visual itch-cues. And it's not just us. Researchers have also studied the contagious effect of itching on monkeys. And, like a yawn being passed back and forth, the monkeys watched another scratch and mirrored the behavior. It might be annoying, but there's also an evolutionary benefit to itching being contagious: when one member of your group is itchy, that might mean they've been exposed to a parasite or there's some kind of irritant around. Which could mean that you've been exposed, too, so it's worth getting a head start on the scratching, just in case.

Thanks to Patreon patrons James C., Eugene K., Alessia Alessandra, Robert Watson, and Lorenzo, who all asked us this question! And thanks to all of our patrons, who keep these answers coming. If you'd like to submit a question to be answered, just go to patreon.com/scishow. And don't forget to go to youtube.com/scishow and subscribe!