The Science of Disgust

Photo: Cherdchanok Treevanchai/Getty Images

It turns out that you don’t need a thick self-help book in order to “change your thoughts.” All you need is a bottle of — wait for it — fart spray. Not a big vial either, just a small whiff of “real fart” smell. This is according to David Pizarro, professor of psychology at Cornell University, who investigated whether the smell of something disgusting could affect people’s judgment.

Pizarro’s experiment builds upon a growing body of research that shows disgust, once labeled the “forgotten emotion of psychiatry,” is far more influential in shaping our beliefs, bonds, and behavior than previously thought.

What is disgust?

Disgust is a universal emotion that bubbles up when we feel aversion toward something offensive or potentially contaminating. This can be something we perceive via our physical senses, actions or appearances, or even ideas and opinions.

As with other emotions, disgust has a range of states with varying intensities, from mild dislike to intense loathing:

Source: Atlas of Emotions

While certain triggers for disgust are universal, for instance coming into contact with bodily products (vomit, phlegm/mucus, feces/diarrhea, blood) or animality (slugs, snakes, maggots, rats, and cockroaches), other triggers are more culturally or personally induced (types of food, perceived perversions).

Disgust has also been labeled the “body and soul” emotion because of its links to morality. Originally, disgust was thought to be a defense mechanism against a physical bodily threat: You eat a bad piece of meat and your body wants to throw it up, so you won’t die. But its purview broadened as we grew into a highly social species.

One defining feature of disgust is that it, more than any other emotion, feels like a “gut” sensation, perhaps because of its link to nausea.

Human beings are disease-carriers, Valerie Curtis, former director of the Hygiene Centre at the London School of Hygiene and Tropical Medicine, explained to me — and as such we have to be very careful about who we come in contact with in order to mitigate disease-transfer risks. The visceral disgust response gives us a mechanism for doing this because instinctively, it causes us to pull away from others who are potential threats.

One defining feature of disgust is that it, more than any other emotion, feels like a “gut” sensation, perhaps because of its link to nausea. This resonates with neuroscientist Antonio Damasio’s somatic hypothesis that bodily reactions such as nausea can become so well learned that the mere thought of, or association with, a similar situation may result in an as if reaction in the brain. Other research also found that inducing bodily disgust evoked memories of related experiences and emotions and/or an awareness of important values or beliefs. It likewise led participants to make more severe and moral judgments.

How disgust can influence our sense of right and wrong

Disgust is also thought to have evolved to protect humans against social threats. That revulsion or gut sensation we get when, for instance, we see someone say or do something that deeply offends us can be a way of establishing normative boundaries to protect our social and moral identities. It can also be a way to distance ourselves from others who would “break the rules” and potentially put us in danger.

Jonathan Haidt, a moral psychologist at New York University Stern School of Business, was one of the first to identify a causal relationship between disgust and morality. His groundbreaking paper in 2001 proposed that gut feelings or unconscious emotions control what we judge to be right and wrong more than rational analysis. Since then, other researchers have followed — like Pizarro, with his fart spray.

In his experiment, Pizarro and the team doused one room with the gross-smelling odor and another without. Then he asked participants in each room to rate their feelings of warmth toward different social groups, including older adults, African Americans, and homosexuals, among others. It’s worth noting that Pizarro did not mention the stench to those in the stinky room.

The results were stark.

On average, the participants shrouded by the stink felt less warmth toward homosexual men compared to those in any other group or those in the nonstinky room. Because other research has shown a link between political affiliation and disgust, Pizarro broke down the results by liberals and conservatives. Though studies show that the more conservative a person is, the harsher their moral judgments are when feeling disgusted, interestingly, the lack of warmth toward gay men in this situation was of equal strength among the two political groups.

Disgust as a weapon of prejudice and persuasion

The result of these and other similar findings bring to light some curious and concerning issues about personal prejudice, and how they could be used to influence or manipulate. “[Disgust] works through association,” said Pizarro in a TEDx talk. “When one disgusting thing touches a clean thing, that clean thing becomes disgusting — not the other way around. This becomes a very useful strategy if you want to convince someone that an object, or an individual or an entire social group ought to be avoided.”

Disgust has even been shown to influence how juries determine guilt or innocence.

Throughout time and across culture, disgust has been used as a weapon to persecute and a way to “otherize.” Nazi propaganda depicted Jews as cockroaches and rats and smelling foul. During the Rwandan genocide, Hutus disparaged Tutsis also as cockroaches. Women (particularly menstruating ones), lower castes, the mentally and physically disabled, homosexuals, and even interracial sex have all been viewed with disgust and, in some circumstances, forced to the margins of society — if not expelled outright.

Politicians have also wielded the power of disgust to influence individuals and groups. In 2010, Carl Paladino, a political activist and Tea Party member, mailed out campaign leaflets that smelled like rotting trash, plastered with the slogan “Something Stinks in Albany” alongside photos of his opponents.

Disgust has even been shown to influence how juries determine guilt or innocence. Research by Sophie Russell at the University of Kent revealed that the feeling of disgust can prevent a juror from taking into consideration mitigating factors, like intent. She also showed that disgust, more than anger, can influence a juror’s judgment.

The brain on disgust— a short-circuit for empathy

Associating an enemy or group with an object of disgust presents meaningful barriers to empathy. Psychologists Susan Fiske and Lasana Harris, at Princeton University, used MRI scans and images of drug addicts and bedraggled people to better understand what happens in the brain when disgust is evoked. Not only did the areas that indicate fear (amygdala) and disgust (insula) activate, but the medial prefrontal cortex, the area that is engaged when we think about other people and social situations (not objects), was less active. Jorge Moll, a cognitive neuroscientist at Rede Labs D’Or in Rio de Janeiro, Brazil, conducted research that suggested that the lateral orbitofrontal cortex, a region of the brain that represents non-reward and punishment, was also activated when participants decided whether to oppose charitable organizations that had moral agendas different from their own, such as abortion, gun control, and the death penalty.

So, is all disgust bad?

Disgust may have its dangers, such as dehumanizing and denigrating others. But defenders of disgust also caution not to dismiss it. Leon Kass, who served as the chairman of the bioethics council under George W. Bush, acknowledged that disgust has been used historically in the persecution of groups; however, he also suggests there is “wisdom in repugnance.” “People should take into account their feelings of disgust, for such feelings tell us about the boundaries that we should not cross.” In this way, Kass argues, disgust can be a useful gauge for interaction with the world.

Pizarro and others don’t disagree; rather, they caution that the only way to ensure that “the gauge” is working properly is to be vigilant in our disgust surveillance. Pizarro told New Scientist, “Even though we might have very strong disgust reactions, we should be tasked with coming up with reasons [to make certain that our assumptions or actions are] independent of this reflexive gut reaction.”

Interestingly, women tend to be more easily disgusted than men, especially in the early months of pregnancy and just after ovulation. The young (starting at about age four) are more likely than older folks to be disgusted (possibly because the senses dull with age or because life experience alters what we rationally deem to be a threat).

While disgust may limit our ability to be empathetic in some cases, studies also show that the disgust response is suspended in response to someone we are close to. Rather than trying to get away from someone we love in an otherwise gross situation, intimacy lowers our disgust threshold, so we are able to help those we care for, no matter how stinky.

Award-winning writer, therapist, clinical ethicist, and researcher specializing in moral injury. I talk about the stuff many won’t. micheledemarco.com

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