Do Not Read This at Lunch

Scientists teased out a new dimension of disgust by showing people gross videos of rotting meat, bugs, and other very unappetizing prospects.

a mosquito drinking blood from a very hairy arm
Henrik Sorensen / Getty

I’ve spent the past few days feeling unusually itchy, mostly thanks to the mosquitoes thriving here on the humid East Coast. A bit of my niggling urge to scratch, though, can be attributed to videos of mosquitoes, including one uploaded to YouTube by someone who thought it would “look cool to record” the insects guzzling his blood. No bugs touched my body as I watched the mosquitoes’ spindly legs tap-dance over his skin, their needle-like mouthparts piercing his flesh. But my fingernails still flew to my arm, as if I had no choice but to drive the invisible pests away.

Are mosquitoes disgusting? Itchy-scritchy ordeals like mine would argue yes, totally, a million times over. Mosquitoes are grody-looking creatures that invade our personal space and make us go at our own flesh and bleed; they can ferry nasty microbes into our vessels, sometimes causing serious disease and death. Disgust, after all, is the emotion that scientists say we evoke to fend off the small and infectious, pathogens and parasites alike.

Disgust, however, is generally linked to retching, gagging, nausea, and other reactions you’d expect to, say, a filthy clogged toilet. These behaviors pretty well capture how we act around internal pathogens; getting gastrointestinally grossed out helps us avoid the yuck, and ups the chances that we don’t get sick from touching it. But according to Tom Kupfer, a psychologist at Nottingham Trent University, in the United Kingdom, that version of disgust (a word that literally means “an aversion to taste”) doesn’t really capture how we act around mosquitoes and the like—ectoparasites that latch onto the outsides of our bodies, and aren’t really deterred by our urge to upchuck.

When Kupfer shows people films of fleas, ticks, and spiders, they do reliably get grossed out. But they don’t often blanch or try to puke. They say that their skin crawls, and that they want to scratch. They report feeling tickles, tingles, and goosebumps, as I did—sensations that just don’t match the classical suite of disgusted behaviors. In English, we don’t really have an official phrase for this feeling—the creepy-crawlies? The heebie-jeebies?—but Kupfer and his colleagues are, for now, terming it a “skin surface” or “surface guarding” response, to capture a new variation on blech.

Their findings are of scientific significance, and a semantic one too. We play fast and loose with the word disgust, but in reality, “there’s a lot more nuance in the things we respond to, and which ones we respond to more strongly,” Tara Cepon Robins, a disgust researcher at the University of Colorado at Colorado Springs who wasn’t involved in the study, told me. Mosquitoes and their allies are gross. But perhaps they’re gross in their own way, and deserve to occupy a separate revolting league.

Kupfer first began digging into these ideas in 2017 while attending a scientific conference focused on pathogen- and parasite-avoidance behaviors, where he met Daniel Fessler, a fellow disgustologist at UCLA. The two got to talking about the grossness of different parasites and pathogens, and how internal and external creepsters had too often been lumped together, or even conflated, by classical disgust. “It simply can’t be that natural selection would fail to refine defenses against these very different classes of threats,” Fessler, an evolutionary anthropologist, told me. The basic idea that bugs make us and other animals flinch, itch, and swat isn’t new, and disgustologists have ventured into this realm before. But Kupfer and Fessler say their recent investigations are the first to run a head-to-head comparison of human responses to skin-crawling parasites and gut-invading pathogens.

After the conference, the pair set up three studies of about 300 to 400 people each: two in the United States, and one in China. They had volunteers watch two sets of videos; one was intended to evoke thoughts of internal microbes, and another focused on ectoparasites. The participants then documented how often they felt classical, oral-gastric disgust (nausea, discomfort in their stomach or throat, urges to gag, and the like) or sensations on their skin (tickling, shaking, itching, etc.).

The videos in both categories were frankly gnarly, and I’m not sure I can recommend them in good conscience. Batting for Team Ectoparasite were several insects and arachnids—fleas, ticks, spiders, mosquitoes, and bed bugs, cavorting atop sad-looking kittens and stretching their legs over stretches of naked skin. Kupfer’s team found that, like me, the volunteers watching these videos fidgeted and scratched; their discomfort was fixated not on their insides but their outsides, where the bugs would have been in real life.

Those reactions largely flipped when the researchers showed clips more in line with OG disgust: infected skin, pus dribbling out of wounds, warts, a rotting pork chop that Kupfer left in his garden for several weeks, and worst of all, a bunch of portable toilets at a music festival that had been filled to the point of overflowing. (Sadly, or luckily, that last clip is no longer available.) “That’s a pretty strong stimulus,” Fessler told me cheerily, minutes after mopping up some “frothy green and yellow” vomit off his floor. (His dog, as if on cue, had puked next to him while we were talking on the phone.) People watching these clips felt nauseated and wanted to gag. Their responses centered on their insides, and on keeping the events they were seeing on film as far away from their stomach as possible.

These discrepancies, other experts told me, match up pretty well with the best ways to keep different pathogens and parasites at bay. Classical disgust has deep roots in ideas of avoidance—keeping unwanted substances out, cloistering ourselves from what could make us ill. But unlike the microscopic pathogens we inadvertently ingest, ectoparasites are the ones chasing us. “Now you have things that are touching you that you didn’t ask for, and that you can’t so much avoid,” Cepon Robins said. Having a separate “barrier response makes a lot of sense.” Zuri Sullivan, an immunologist at Harvard who wasn’t involved in the study, points out that the delineations in this system roughly mirror our immune system’s different responses for microbes, which often try to infiltrate our cells, and for parasites, which tend to bop around outside our cells. Cell-invading microbes (think: viruses) get a “seek and destroy” treatment, Sullivan told me, while parasites (think: worms) are dealt a “weep and sweep” approach, intended to flush them out. Kupfer and Fessler might be watching similar differences play out on a more macro scale.

But the defenses we mount against internal pathogens and external parasites can and do overlap, which might be part of why these sorts of reactions were conflated for so long—and why they’re worth studying together. Biting bugs can chauffeur microbes into our blood. And insect larvae congregate in the same nutrient-rich spots, such as rotting meat, as bacteria, points out Cécile Sarabian, a disgust researcher at the Kyoto University Primate Research Institute who helped organize the conference that brought Kupfer and Fessler together but wasn’t involved in their work. Some people felt both itchy and nauseated when watching the team’s videos; all of it was, to varying degrees, scientifically revolting. “Maybe these things aren’t fully disentangled, but there’s a reason for that,” Diana Fleischman, a disgust researcher and psychologist at the University of Portsmouth who wasn’t involved in the study, told me. These behaviors are, after all, geared toward the same goal of keeping us safe from infectious threats.

Some languages have nailed down a distinction for those creepy-crawly feelings: yuputka, from the Native American language of Ulwa; kinikilabutan in Tagalog; huivering in Dutch. I asked several people how we might incorporate the idea of ectoparasite defense into the English lexicon—whether it’s worth expanding the scientific definition of disgust, or finding some new words that nod to the sensations’ skin-centric bent. There was, unsurprisingly, no consensus. Like other emotions, disgust is context-dependent, fluid across cultures and situations; the word itself was not, as Kupfer points out, designed for scientific purposes. Linguistics aside, though, it’s still helpful to know why we react the way we do, and whether those warning signs center on our stomach or our skin. It is, in other words, totally fine that I don’t have a good term for the sensations I feel when insect legs scamper over my skin—as long as I better understand why I feel them at all.