Publisher Health

To hear more audio stories from publications like The New York Times, download Audm for iPhone or Android.

Two distinguished academics walk into a restaurant in Manhattan. It is their first meeting — their first date, in fact — and the year is 2015. The man wears a down jacket against the icy winter evening. The woman has a shock of glossy white hair. The restaurant is on a cozy corner of the West Village and has foie gras on the menu. What the man doesn’t know is that the interior of his down jacket has suffered a structural failure, and the filling has massed along the bottom hem, forming a conspicuous bulge at his waist. As they greet each other, the woman perceives the bulge and asks herself: Is my date wearing a colostomy bag?

They sit down to eat, but the woman is distracted. As they chat about their lives — former spouses, work, interests — the woman has “colostomy bag” on her mind. Is it or isn’t it? The two academics are of an age where such an intervention is, well, not exactly common, but not out of the realm of possibility. At the end of their dinner, the man takes the train back to Philadelphia, where he lives, and the woman returns to her apartment on the Upper West Side. Despite the enigma of the man’s midsection, the date is a success.

It wasn’t until their third date that the question got resolved: no colostomy bag. “I was testing her,” Paul Rozin, one of the academics, later joked, “to see if she would put up with me.” (He wasn’t testing her. He was unaware of the bulge.) “I was worried,” said Virginia Valian, the other academic.

It was fitting that an imaginary colostomy bag played a starring role in the couple’s first encounter. Paul Rozin is known for many things — he is an eminent psychologist who taught at the University of Pennsylvania for 52 years, and he has gathered honors and fellowships and published hundreds of influential papers and served on editorial boards and as chairman of the university’s department of psychology — but he is best known for his work on the topic of disgust. In the early 1980s, Rozin noticed that there was surprisingly little data available on this universal aspect of life. Odd, he thought, that of the six so-called basic emotions — anger, surprise, fear, enjoyment, sadness, disgust — the last had hardly been studied.

Once you are attuned to disgust, it is everywhere. On your morning commute, you may observe a tragic smear of roadkill on the highway or shudder at the sight of a rat browsing garbage on the subway tracks. At work, you glance with suspicion at the person who neglects to wash his filthy hands after a trip to the toilet. At home, you change your child’s diaper, unclog the shower drain, empty your cat’s litter box, pop a zit, throw out the fuzzy leftovers in the fridge. If you manage to complete a single day without experiencing any form of disgust, you are either a baby or in a coma.

Disgust shapes our behavior, our technology, our relationships. It is the reason we wear deodorant, use the bathroom in private and wield forks instead of eating with our bare hands. I floss my teeth as an adult because a dentist once told me as a teenager that “Brushing your teeth without flossing is like taking a shower without removing your shoes.” (Do they teach that line in dentistry school, or did he come up with it on his own? Either way, 14 words accomplished what a decade of parental nagging hadn’t.) Unpeel most etiquette guidelines, and you’ll find a web of disgust-avoidance techniques. Rules governing the emotion have existed in every culture at every time in history. And although the “input” of disgust — that is, what exactly is considered disgusting — varies from place to place, its “output” is narrow, with a characteristic facial expression (called the “gape face”) that includes a lowered jaw and often an extended tongue; sometimes it’s a wrinkled nose and a retraction of the upper lip (Jerry does it about once per episode of “Seinfeld”). The gape face is often accompanied by nausea and a desire to run away or otherwise gain distance from the offensive thing, as well as the urge to clean oneself.

The more you read about the history of the emotion, the more convinced you might be that disgust is the energy powering a whole host of seemingly unrelated phenomena, from our never-ending culture wars to the existence of kosher laws to 4chan to mermaids. Disgust is a bodily experience that creeps into every corner of our social lives, a piece of evolutionary hardware designed to protect our stomachs that expanded into a system for protecting our souls.

Darwin was the first modern observer to drop a pebble into the scummy pond of disgust studies. In “The Expression of the Emotions in Man and Animals,” he describes a personal encounter that took place in Tierra del Fuego, where Darwin was dining on a portion of cold preserved meat at a campsite. As he ate, a “naked savage” came over and poked Darwin’s meat with a finger, showing “utter disgust at its softness.” Darwin, in turn, was disgusted at having his snack fingered by a stranger. Darwin inferred that the other man was repelled by the unusual texture of the meat, but he was less confident about the origins of his own response. The hands of the “savage,” after all, did not appear to be dirty. What was it about the poking that rendered Darwin’s food inedible? Was it the man’s nakedness? His foreignness? And why, Darwin wondered — moving on to a remembered scenario — was the sight of soup smeared in a man’s beard disgusting, even though there was “of course nothing disgusting in the soup itself”?

The most important disgust accounts following Darwin come from a pair of Hungarian men born two years apart, Aurel Kolnai (born in 1900) and Andras Angyal (1902). I haven’t found any evidence that they knew each other, but it seems improbable that Angyal, whose disgust paper came out in 1941, didn’t draw from his countryman’s paper, which appeared in 1929. Strangely enough, the Angyal paper contains no reference to Kolnai. One possibility is that Angyal failed to cite his sources. A second possibility is that he was truly unaware of the earlier paper, in which case you have to wonder whether there was something so abnormally disgusting about Central Europe of the early 20th century that two strangers born there were driven to lengthy investigations of a subject no one else took seriously.

A third possibility is that Angyal started reading Kolnai’s paper and gave up midway through in frustration. While brilliant, Kolnai’s writing has the density of osmium. His paper is rife with scare quotes and clauses layered in baklava-like profusion. Nonetheless, Kolnai was the first to arrive at a number of insights that are now commonly accepted in the field. He pointed to the paradox that disgusting things often hold a “curious enticement” — think of the Q-tip you inspect after withdrawing it from a waxy ear canal, or the existence of reality-TV shows about plastic surgery, or “Fear Factor.” He identified the senses of smell, taste, sight and touch as the primary sites of entry and pointed out that hearing isn’t a strong vector for disgust. “One would search in vain for any even approximately equivalent parallel in the aural sphere to something like a putrid smell, the feel of a flabby body or of a belly ripped open.”

For Kolnai, the exemplary disgust object was the decomposing corpse, which illustrated to him that disgust originated not in the fact of decay but the process of it. Think of the difference between a corpse and a skeleton. Although both present evidence that death has occurred, a corpse is disgusting where a skeleton is, at worst, highly spooky. (Hamlet wouldn’t pick up a jester’s rotting head and talk to it.) Kolnai argued that the difference had to do with the dynamic nature of a decomposing corpse: the fact that it changed color and form, produced a shifting array of odors and in other ways suggested the presence of life within death.

Angyal argued that disgust wasn’t strictly sensory. We might experience colors and sounds and tastes and odors as unpleasant, but they could never be disgusting on their own. As an illustration, he related a story about walking through a field and passing a shack from which a pungent smell, which he took for that of a decaying animal, pierced his nostrils. His first reaction was intense disgust. In the next moment, he discovered that he had made a mistake, and the smell was actually glue. “The feeling of disgust immediately disappeared, and the odor now seemed quite agreeable,” he wrote, “probably because of some rather pleasant associations with carpentry.” Of course, glue back then probably did come from dead animals, but the affront had been neutralized by nothing more than Angyal’s shifting mental associations.

Disgust, Angyal contended, wasn’t merely smelling a bad smell; it was a visceral fear of being soiled by the smell. The closer the contact, the stronger the reaction. Angyal’s study is even more delightful when viewed in the context of its preface, which explains that the material is based on observations and conversations “not collected in any formal manner,” and that the method, “if it may be called such,” lacked objectivity and control. Reading the paper 80 years later, as a replication crisis in the sciences continues to unfold, Angyal’s humility takes on a refreshing flavor. I’m just a guy noticing some stuff, he seems to say. Let’s see where this leads.

I first met Rozin at a Vietnamese restaurant on the Upper West Side in midsummer. He arrived in a bucket hat the color of Tang and a navy shirt with pinstripes. After ordering, we sat at a blond wood table and ate rice crepes piled with diverse vegetable elements. Rozin had ordered a green-papaya salad to share, and while spearing papaya he noted that “this, right now, is a form of social bonding — eating from the same bowl.” (He and a team did a study on it.) A fun thing about hanging out with a research psychologist is that he can usefully annotate all sorts of immediate lived phenomena, and in the case of Rozin, he may even have hypothesized the explanations himself. Our crepes, to take an example, were the width of basketballs — enough to feed six, easily — and yet we each polished off the jumbo portion. “Unit bias” is the heuristic that Rozin and his co-authors coined to describe the effect back in 2006. The idea is that humans tend to assume a provided unit of some entity is the proper and optimal amount to consume. This is why movie popcorn and king-size candy bars are treacherous, and possibly one reason French people — with their traditionally small portions — remain thin.

Rozin, who is now 85, was born in the Flatbush neighborhood of Brooklyn to Jewish parents who, though they hadn’t attended college themselves, were cultured and artistic and pleased to discover that their son was a brainiac. He tested into a public school for gifted children, left high school early and received a full scholarship to the University of Chicago, where he matriculated just after his 16th birthday. Upon graduating, he took a joint Ph.D. at Harvard in biology and psychology, completed a postdoc at the Harvard School of Public Health and in 1963 joined the faculty of the University of Pennsylvania, where his initial experiments centered on behavior in rats and goldfish. As he quickly worked his way up from assistant professor to associate professor to full professor, Rozin decided that he was tired of animal studies and wanted to focus on bigger game.

Around 1970, he turned his attention to the acquisition of reading. In Philadelphia — as in many American cities — there was a problem with kids’ learning to read. Eager to discover why, Rozin parked himself in elementary-school classes and observed something strange: A large number of children were unable to read by second grade, but those same children were always fluent in spoken English. They could name thousands of objects, and they could point to Rozin and ask, “Why is this strange man lurking in my classroom?” Compared with the vast dictionary of words filed neatly in their brains, mastering an alphabet of 26 letters would seem to be a piece of cake. Instead, it was a crisis. With a collaborator, Rozin devised an experimental curriculum that moved children through degrees of linguistic abstraction by teaching them Chinese logographs followed by a Japanese syllabary, and only then applying the same logic to English. Rozin says the system worked like a dream, but the school’s response was tepid.

“The bureaucracy, the politics — I was overwhelmed,” he said. Nothing about the process of pitching and marketing and lobbying appealed to him. He calculated that it would take years to sell administrators on the curriculum and train teachers to deliver it. Instead, he and a colleague wrote several papers with the findings and walked away. “It’s the right way to teach reading,” he said nearly 50 years later, with a shrug. “As far as I know, nothing happened with it.” At the time, he wondered if maybe some other researchers would run with the idea. But Rozin was done. His mind was elsewhere, percolating on the subject he would become best known for.

Rozin’s interest in disgust, he said, started with meat. Although he is now pescatarian “with some exceptions” (bacon), he was still a full-spectrum omnivore when he started puzzling over meat. Despite being one of the world’s favorite food categories — both nutritionally complete and widely considered tasty — meat is also the most tabooed food across many cultures. Rozin wasn’t interested in the health implications of meat or in its economic or environmental significance. That stuff had been studied. What he zeroed in on was a kind of affective negativity around meat. When people disliked it, they really disliked it. A rotten cut of beef evoked an entirely different reaction than a rotten apple. Why? Or rather, what? What was the difference between accidentally biting into a moldy Granny Smith and a moldy steak? A bad apple might be icky and distasteful, but befouled meat caused a related, but totally distinct, sensation cluster of contamination, queasiness and defilement.

‘Now I’m going to take this sterilized, dead cockroach, it’s perfectly safe, and drop it in this juice glass.’

It was the Angyal paper that really got Rozin’s neurons firing, and on its foundation he began to construct the theory that would go on to inform — and this is no exaggeration — every subsequent attempt at defining and understanding disgust over the following decades. In Rozin’s view, the emotion was all about food. It began with the fact that humans have immense dietary flexibility. Unlike koalas, who eat almost nothing but eucalyptus leaves, humans must gaze at a vast range of eating options and figure out what to put in our mouths. (The phrase “omnivore’s dilemma” is one of Rozin’s many coinages. Michael Pollan later borrowed it.) Disgust, he argued, evolved as one of the great determinants of what to eat: If a person had zero sense of disgust, she would probably eat something gross and die. On the other hand, if a person was too easily disgusted, she would probably fail to consume enough calories and would also die. It was best to be somewhere in the middle, approaching food with a healthful blend of neophobia (fear of the new) and neophilia (love of the new). It was Rozin’s contention that all forms of disgust grew from our revulsion at the prospect of ingesting substances that we shouldn’t, like worms or feces.

The focus on food makes intuitive sense. After all, we register disgust in the form of nausea or vomiting — nausea being the body’s cue to stop eating and vomiting our way of hitting the “undo” button on whatever we just ate. But if disgust were solely a biological phenomenon, it would look the same across all cultures, and it does not. Nor does it explain why we experience disgust when confronted with topics like bestiality or incest, or the smell of a stinky armpit, or the idea of being submerged in a pit of cockroaches. None of these have anything to do with food. Rozin’s next project was to figure out what linked all of these disgust elicitors. What could they possibly have in common that caused a unified response?

In 1986, Rozin and two colleagues published a landmark paper called “Operation of the Laws of Sympathetic Magic in Disgust and Other Domains,” which argued that the emotion was a more complicated phenomenon than Darwin or the Hungarians or even Rozin himself had ventured. The paper was based on a series of simple but illuminating experiments. In one, a participant was invited to sit at a table in a tidy lab room. The experimenter, seated next to the participant, unwrapped brand-new disposable cups and placed them in front of the subject. The experimenter then opened a new carton of juice and poured a bit into the two cups. The participant was asked to sip from each cup. So far, so good. Next, the experimenter produced a tray with a sterilized dead cockroach in a plastic cup. “Now I’m going to take this sterilized, dead cockroach, it’s perfectly safe, and drop it in this juice glass,” the experimenter told the participant. The roach was dropped into one cup of juice, stirred with a forceps and then removed. As a control, the experimenter did the same with a piece of plastic, dipping it into the other cup. Now the participants were asked which cup they’d rather sip from. The results were overwhelming (and, frankly, predictable): Almost nobody wanted the “roached” juice. A brief moment of contact with an offensive — but not technically harmful — object had ruined it.

In another experiment, participants were asked to eat a square of chocolate fudge presented on a paper plate. Soon after, two additional pieces of the same fudge were produced: one in the form of “a disc or muffin” and the other shaped like a “surprisingly realistic piece of dog feces.” The subjects were asked to take a bite of their preferred piece. Again, nearly no one wanted the aversive stimuli, which is how psychologists refer to “nasty stuff.” (When asked about the outliers who opted for the nasty stuff, Rozin waved a hand and said, “There’s always a macho person.”)

These results might seem obvious, but the experiments were designed rather craftily to elicit a disgust response rather than any of the other typical food-rejection responses, which include distaste (rejecting something because it looks or smells bad, like broccoli if you’re a broccoli hater) or danger (rejecting something because it might harm you, like a poisonous mushroom or a nonsterilized cockroach) or inappropriateness (rejecting something because it is not considered food, like tree bark or sand). Disgust was unlike the other three responses in one peculiar fashion: It could be motivated primarily by ideational factors — by what a person knew, or thought she knew, about the object at hand.

Until this point, sympathetic magic had been a term psychologists used to account for magical belief systems in traditional cultures, such as hunter-gatherer societies. Sympathetic magic features a handful of iron laws. One is the law of contagion, or “Once in contact, always in contact.” The sterilized roach juice demonstrated this law; if you stuck the “roached” juice in a freezer and offered it to participants a year later, they still wouldn’t drink it. A second is the law of similarity, or “Things that appear similar are similar. Appearance equals reality.” That would be the dog-doo fudge.

Rozin and his colleagues went on to invent other scenarios to test their theories. Would people drink apple juice if it was served in a brand-new bedpan? Would they sip a favorite soup if it had been stirred by a used but “thoroughly washed” fly swatter? Would they touch a new, unused tampon to their lips? Would they wear an actual vintage Nazi hat with a swastika on it?

The 1986 paper was the equivalent of a sculptor’s cutting down a statue’s raw form from a mammoth block of marble, and the papers Rozin published in its aftermath were the chisel-maneuvering that revealed a detailed anatomy underneath. In work published the next year, he observed that some of our disgust responses might be adaptations designed to avoid pathogens. Under this logic, a person who swerves to avoid the blast radius of a sick person’s sneeze is likely to survive and produce offspring who will themselves avoid sneeze radii.

Rozin also elaborated what he called the “animal reminder” theory, which posits that disgust is a way to strenuously ignore the mountain of evidence that humans are, in fact, mammals who eat, excrete, bleed, rut and die just like every other mammal. Our hygiene laws require that we avoid playing with our own feces, as dogs do. Our sexual laws require that we refrain from having sex with our siblings, like cats, or copulating with the dead, like certain snakes, or cannibalizing our children, like rabbits. Adhering to such purity rules goes a long way toward minimizing awareness that our bodily temple is only a meat suit. One of Rozin’s most intriguing theories is that disgust operates as a foreshadowing of our own deaths. Every encounter with moldy meat is a sneak preview of the fact that we will all, at some point, become moldy meat ourselves.

Both the reality-puncturing and social elements of disgust make it ripe for comedy. Take this monologue from a 1995 “Seinfeld” episode:

Jerry: “Now, I was thinking the other day about hair — and that the weird thing about it is that people will touch other people’s hair. You will actually kiss another human being, right on the head. But, if one of those hairs should somehow be able to get out of that skull, and go off on its own, it is now the vilest, most disgusting thing that you can encounter. The same hair. People freak out. There was a hair in the egg salad!”

Seinfeld’s point about rogue hairs also goes for fingernails, dandruff and other anatomical flotsam, whether it be our own (grosser the longer we’ve been separated from it) or someone else’s (always gross). What we consider innocuous when attached to the body or housed snugly within it — snot, spit, pee — becomes a pollutant only when it bursts free from its container.

In 1994, Rozin and two co-authors came up with a 32-item disgust scale to measure a person’s sensitivity to the emotion. By this time, he was proposing seven domains of disgust: food, animals, body products, sexual deviance, what he called “body-envelope violations” (i.e., gore), poor hygiene and contact with death. The first portion of the test consisted of true-or-false statements like “I might be willing to try eating monkey meat, under some circumstances” and “It would not upset me at all to watch a person with a glass eye take the eye out of the socket.” The second portion asked that a person rate how disgusting she might find certain experiences, such as “You discover that a friend of yours changes underwear only once a week” or “You are walking barefoot on concrete, and you step on an earthworm.”

At 7.5, Rozin’s own score was much lower than the average of 17. This was borne out in our interactions. At dinner one night, Rozin pulled out his iPhone to share photos of a meal that one of his sons, an amateur chef, had prepared: deep-fried tarantulas, crickets in chili sauce, mealworms sautéed in olive oil. Dessert was a plate of imitation turds molded from chocolate cake. “One of them was coiled,” Rozin said of the cakes, zooming in. “It was a lot of fun.”

Later that night, the topic of funerals came around. Rozin explained that he hadn’t yet decided what to do with himself, so to speak, after his own death. “Historically, most cannibals ate their ancestors,” he said. “I mean, they ate them after they died; they didn’t kill them.” He acknowledged that ritual cannibalism held little appeal to the average person, but he thought the underlying concept had a certain beauty. “When my ex-wife died, she was cremated, and we were burying her ashes under a tree in the backyard,” he said. “And I felt I had to eat some.”

“Why?” I asked, as Rozin buttered a piece of baguette.

“To assimilate some of the person I loved very much,” Rozin replied, as though it were obvious. “This is good bread, by the way.”

One constant of disgust discourse over the past two centuries is that people have loved to claim that their period is the most disgusting period that ever existed. Obviously this can’t be true. It’s unthinkable that any era since the advent of modern sanitation could be more disgusting than the thousands of years preceding it. Yes, it is now easy to buy vomit-flavored jelly beans at your local Walmart and to watch internet videos of people being decapitated. But these are elective activities. The scenarios that perhaps carry the highest disgust payload — like caring for the sick — now largely occur in institutions, not homes. Garbage is sealed in odor-resistant bags. Our waste vanishes seconds after its production, whisked down an invisible network of pipes to tanks and treatment facilities.

“Part of disgust is the very awareness of being disgusted, the consciousness of itself,” the scholar William Ian Miller wrote in 1997. “Disgust necessarily involves particular thoughts, characteristically very intrusive and unriddable thoughts about the repugnance of that which is its object.” In other words, you can’t be disgusted without knowing that you’re disgusted. Relatedly, there’s no unambiguous evidence that nonhuman animals experience disgust. Distaste, yes. Dislike, yes. But the capacity to be disgusted is, as Miller put it, “human and humanizing.” Those with ultrahigh thresholds are those whom “we think of as belonging to somewhat different categories: protohuman like children, subhuman like the mad or suprahuman like saints.” The 14th-century saint Catherine of Siena is famous for drinking the pus of a woman’s open sore in an act of holy self-abasement.

The theorist Sianne Ngai has written about disgust as a social feeling. A person in the thick of it will often want her experience confirmed by other people. (As in: “Oh, my God, this cheese smells disgusting. Here, smell it.”) More recently, researchers have shown that disgust is an accurate predictor of political orientation, with conservatives displaying a far higher disgust response than liberals. In a 2014 study, participants were shown a range of images — some disgusting, some not — while having their brain responses monitored. With great success, researchers could predict a person’s political orientation based on analysis of this f.M.R.I. data.

Rozin’s most famous student is Jonathan Haidt, the social psychologist and co-author of “The Coddling of the American Mind,” who received his Ph.D. from the University of Pennsylvania and collaborated with Rozin on a number of papers. “I came to see him because I was studying moral psychology, and I hadn’t really thought about disgust,” Haidt told me over the phone. “But when I started reading ethnographies, I saw they almost all had purity and pollution norms. Tons of rules — about menstruation, how you handle corpses, sexual taboos, food taboos.” Western societies, he noticed, were the global exception in their lower regulation of disgust-related activities. But then, this wasn’t entirely true, Haidt realized; within America, there were plenty of groups that legislated bodily practices related to disgust, like Orthodox Jews and Catholics and, to a lesser degree, social conservatives. It was only among Western secular progressives that disgust remained somewhat lawless.

Haidt continued to zero in on the political uses of the word, noticing that Americans often listed as “disgusting” such things as racism, brutality, hypocrisy and ambulance-chasing lawyers. “Liberals say that conservatives are disgusting. Conservatives say that welfare cheaters are disgusting,” he wrote in a paper with Rozin and two others in 1997. What was that about? Was the use of “disgust” for such a wide range of activities simply a metaphoric quirk of the English language? Did the pundits who sat around all day expressing disgust on TV have to keep a vomiting bucket next to their desks, or were they just being linguistically imprecise?

Neither, exactly. When Haidt and Rozin looked at other languages, they found that many contained words with a compound meaning equivalent to “disgust” — single words that could be applied to both legislation and diarrhea. German had ekel. Japanese had ken’o. Bengali had ghenna. Hebrew had go-al. When an Israeli woman was asked what situations made her feel go-al, she cited “a horrible accident and you see body parts all over the place” and a person “who just picked his nose and ate it later.” But she also said that “If you really dislike a politician, you would use the word go-al.”

If the initial function of disgust was like a piece of caution tape plastered over our mouths, the tape had — over time — wound itself around our other holes (to regulate sexual activity) and our minds (to regulate moral activity). This potency of the emotion is such that a single anecdote can taint an entire presidential campaign. You may remember a 2019 story about how Senator Amy Klobuchar once ate a salad with a comb. According to the article, an aide purchased a salad for Klobuchar at an airport. Later, when the senator wanted to eat her salad on the plane, she discovered that there were no utensils available. After berating the aide, Klobuchar retrieved a comb from her purse and (somehow) ate her salad with it. When finished, she handed the comb to her aide with orders to clean it.

The comb story was part of a larger narrative about the senator’s treatment of her staff, which Klobuchar bravely tried to spin into evidence of her exactitude. You have to admire the effort, but the senator’s defense was useless. Nobody came away thinking that her mistake was in having high expectations. Her mistake was in doing something gross in front of multiple witnesses. That image was indelible. You couldn’t read the story without imagining the comb, a hair perhaps still caught in its teeth, plunging into an oily airport salad. Like all disgusting stories, it had a contaminating effect. Now the anecdote was in you, the voter. The taste of the comb was upon your own tongue, and you had no choice but to resent Klobuchar for putting it there.

The episode belongs to a list of disgust-related political scandals: the pubic hair on the Coke can, the stain on the blue Gap dress. On a recent weekend I passed a truck in Queens with a giant bumper sticker that said, “Any Burning or Disrespecting of the American Flag and the driver of this truck will get out and knock you the [expletive] OUT.” This was a perfect Haidt litmus test. A liberal might walk past the truck and think some version of: This guy — and it’s definitely a guy — has an anger problem. A conservative might walk past the truck and think: This guy — and it’s definitely a guy — must really love our country. As Haidt put it: “There are people for whom a flag is merely a piece of cloth, but for most people, a flag is not a piece of cloth. It has a sacred essence.” If a person views the American flag as a rectangle of fabric, it is unfathomable to be disgusted by its hypothetical desecration. If a person views the flag as a sacred symbol, it is unfathomable to not feel this way.

These two types of human — which broadly map onto “liberal” and “conservative,” or “relatively disgust-insensitive” and “relatively disgust-sensitive” — live in separate moral matrices. If it seems bizarre that disgust sensitivity and politics should be so closely correlated, it’s important to remember that disgust sensitivity is really measuring our feelings about purity and pollution. And these, in turn, contribute to our construction of moral systems, and it is our moral systems that guide our political orientations.

To ward off disgust, we enact purity rites, like rinsing the dirt from our lettuce or “canceling” a semipublic figure who posted a racist tweet when she was a teenager. We monitor the borders of mouth, body and nation. In “Mein Kampf,” Adolf Hitler described Jews as like “a maggot in a rotting body” and “a noxious bacillus.” Another category of humankind consistently deemed repulsive is women; to take one of several zillion illustrations, one reason long skirts were a dominant fashion in Western Europe for centuries, according to the fashion historian Anne Hollander, was to conceal the bottom half of the body and by extension its sexual organs. Mermaids aren’t just a folkloric figure but the expression, Hollander argues, of a horrified disgust at the lower female anatomy, which is seen as amphibiously moist and monstrous.

But purification rites may also be healthful (washing your hands) or ritually significant (baptism). We will never disentangle ourselves from the instinct to purify, even as we name different reasons for doing it: justice, patriotism, progress, tradition, freedom, public health, God, science. Beneath it all will be a confused omnivore, stumbling upon a dewy mushroom in the forest — with no clue what will happen if she eats it.

One of Rozin’s greatest coinages is “benign masochism,” which describes any experience that is pleasurable not despite being unpleasant but because of its unpleasantness. Horror movies, roller coasters, deep tissue massage, bungee jumping, hot chili peppers, frigid showers and tragic novels all fit into the category. I can think of some additional edge cases, like acupuncture or the films of John Waters. Rozin pointed out, during dinner one night, that “many people like to look at their own [expletive] after they make it in the toilet. There is a fascination. All the humor. It’s probably related to benign masochism.”

The idea is that these experiences offer a similar excitement, in that they cause fear or pain or repulsion without posing any real existential threat. Our ability to withstand “safe” menaces yields a gratifying sense of mastery. It’s a meta-experience: When you gobble a ghost pepper or cue up “The Exorcist,” you get to experience yourself experiencing something, and you extract enjoyment from your ability to forge a gap between what should feel bad but instead, through sheer will, feels fun.

As with disgust, benign masochism is a uniquely human experience. There’s no evidence that dolphins or coyotes or elephants indulge in it. The paper Rozin and a team wrote about it took me several days to comprehend and served as an example of the subject at hand: an immense irritant with only abstract and hard-won rewards. Chili peppers make you sweat; tragic novels make you cry; academic papers embalm you in a formaldehyde of words and then give you a splendid phrase to use for the rest of your life.

My personal mother lode of benign masochism — and perhaps yours, in the near future — is the F.D.A.’s “Food Defect Levels Handbook,” which is designed for food manufacturers but is available online for anyone to browse, which I do often. It outlines the amount of disgusting matter in a given food that will trigger enforcement action — meaning that any less is just fine. Commercially produced peanut butter, the site will tell you, is allowed to contain anything fewer than 30 insect fragments and one rodent hair per 100 grams. A can of mushrooms may house fewer than 20 maggots. Fewer than a quarter of salt-cured olives in a package may be moldy. A clever entrepreneur could establish a weight-loss program entirely on the basis of alerting people to the larvae and dry rot and beetle eggs that adulterate their favorite foods. But who wants to live that way? The best bulwark against disgust — the only bulwark against so much of life’s wretchedness — is, in the end, denial.

Molly Young is a contributing writer for the magazine and a book critic for The New York Times.