When I first moved to the United Kingdom a few years ago and began house-hunting, I realized that the typical décor inside homes here is slightly different from what you would expect to find in the average American household. Based on the overabundance of shag carpets generously speckled with flicks of vomit-colored hues, the redundant stylistic motifs of concentric circles and the cloying use of linoleum flooring, it would appear the seventies never really left this part of the world. My partner and I found ourselves on more than one occasion turning to each other upon entering one of these homes and whispering with slightly curled upper lips, “disgusting.”

Now this isn’t the place to discuss British aesthetics and I imagine many Europeans would find certain American decorative styles equally vulgar or at least pretentious, but I would like to turn your attention to our use of the word “disgusting” in this context. One of the more interesting sideline debates in psychological science today concerns whether the core emotion of disgust, which involves an aversion to physical contaminants such as bodily waste products, has extended emotionally into other non-contagion domains. For example, my partner, Juan, uses the expression “that’s disgusting” rather frequently—he uses it to describe hairstyles he dislikes, clothes he abhors and architecture he finds offensive. And many people use similar expressions to describe other people or behaviors that violate some social norm.

Quick—what’s the first word that comes to your mind when you conjure up a child molester? If it’s not “disgusting,” it’s probably something similar like “vile,” “repulsive,” “gross” or “nasty.” Some scholars, such as psychologist Paul Bloom from Yale University, believe that our use of these terms in such non-contaminative contexts is only metaphorical for our anger or dislike. That is to say, Bloom and others reason that we don’t really feel nauseated when we use such words in the social domain—not like we do when we come into contact with someone else’s feces or, in my case, when I nearly step on vomit courtesy of a Queen’s undergraduate student who’d imbibed too much Guinness the evening prior. Rather, Bloom believes that these affectively charged terms invoke the element of disgust in the social domain because they transmit our feelings about things we strongly dislike.

One researcher who believes this type of language goes beyond mere metaphor is Bruce Hood, a psychologist at the University of Bristol. In his soon-to-be-released book SuperSense, Hood argues that human beings are prone to reasoning as though other people have a hidden essence that can be transmitted through physical contact

And in a recent issue of the journal Emotion, psychologists Andrew Jones and Julie Fitness from Macquarie University provide some of the first evidence that, at least when it comes to our thinking about social deviants such as sex offenders, thieves and other criminals, we genuinely feel as though these transgressors are a potential source of physical contamination. In fact, this new work on moral disgust builds on a body of theoretical ideas and other research findings suggesting that human beings reason as though social deviants have the equivalent of cooties. The first scholarly statement I’m aware of that mentions this phenomenon was made by the famous sociologist Erving Goffman in his 1963 book Stigma, in which he noted that people wanted on criminal warrants were once referred to as “having smallpox” and their criminal disease was said to be catching; merely being seen with them could lead to arrest on suspicion.

In 1994 psychologist Paul Rozin of the University of Pennsylvania and his colleagues discovered that most study participants expressed repugnance at the thought of wearing serious criminals’ thoroughly laundered clothing. (Just ask yourself whether you’d be comfortable wearing a pedophile’s undershirt or a rapist’s socks.) And in a 2006 study published in Science, Chen-Bo Zhong from the University of Toronto and Katie Liljenquist from Northwestern University reported the peculiar “Macbeth effect” finding. In this study, people who were asked to privately think about their own personal past transgressions (e.g., cheating on their partners, stealing money, mistreating their parents) tended to choose personal hygiene gifts for their participation in the study. That is to say, unlike those in the control group who thought about more innocent things, those who had just reflected on their moral shortcomings were significantly more likely to choose antiseptic wipes as a going-away prize versus an object of equal value, as though they were literally motivated to wipe away their sins.

In one of Jones and Fitness’s studies published last year in Emotion, half of the participants were randomly assigned to a “criminal condition,” whereby they saw a person’s mug shot and read a brief description of this person’s alleged criminal behaviors. The other participants in the study saw the exact same photos, but read fictitious newspaper stories about this person being in a table tennis match or announcing his engagement.

After being exposed to either the criminal story or the boring newspaper story, all participants were then asked to complete a word-completion task. This involves seeing a series of word fragments on a computer screen and being asked to complete the word by filling in the gaps. For example, if you saw W_SH you could either plug in an “I” for “wish” or an “A” for “wash.” Likewise, STIN_ could be either “stink” or “sting.” Jones and Fitness found that participants in the criminal condition were significantly more likely to complete these fragments using washing/disgust terms (such as “wash” and “stink”) than their likely alternatives (such as “wish” and “sting”). And, as in the findings reported by Zhong and Liljenquist, the people who’d just read about the criminals were significantly more likely than the control participants to choose the hygiene-related parting gifts (soap instead of a pen holder) at the end of the study.

Together, this line of research reveals that many people genuinely feel “dirty” and “unclean” when pondering both their own and others’ sins. However, it is unclear whether this subjective reaction to moral contaminants serves a biologically adaptive function or whether it’s a sort of hiccup of our mental evolution—a case of our psychological wiring for reasoning about physical contaminants getting crossed with our social reasoning about moral behaviors. Most scholars studying disgust have argued for the former: that disgust felt toward social deviants was evolutionarily adaptive because it led to their expulsion from the group. Because transgressors compromised the integrity of the group, this disgust was a useful social emotion. It also served as a powerful deterrent to crime, since one would be motivated to refrain from doing things that caused him or her to be the subject of such contempt.

Interestingly, individual differences in “disgust sensitivity” in the domain of nonsocial core disgust tend to predict moral attitudes and even political orientation. Some research findings suggest that people who score high on measures of disgust sensitivity (that is to say, they’re easily grossed out by physical contaminants) also tend to score high on measures of political “right wing authoritarianism” (RWA). According to Jones and Fitness, RWA describes “a personality style and attitudinal orientation characterized by uncritical submission to authority, conventionalism and hostility toward those who are seen as challenging the social and moral orders.”

In line with this idea, psychologist Jonathan Haidt from the University of Virginia has argued that moral judgments are often the product of emotional aversion rather than carefully thought-out reasoning. For example, a whole host of researchers are busy exploring the relationship between disgust sensitivity and homophobic attitudes. Regardless of how they may explicitly justify their beliefs on the subject, most people who believe that homosexuality is wrong also experience disgust at the thought of gay sex. Much of this work suggests it is the gut-level feeling of disgust that leads homophobes to reason that the behavior is immoral, not the other way around. In other words, “that which disgusts me must be wrong” rather than “it is wrong, therefore I should be disgusted.”

Personally I find straight sex a little off-putting, but I say whatever floats your boat. Now if only I can find a house in Northern Ireland where the floral wallpaper doesn’t have me running to the toilet and the carpet design doesn’t induce epileptic seizures, my gay lover and I will be snug as two sinful bugs in a thoroughly clean rug.

In this new column presented by Scientific American Mind magazine, research psychologist Jesse Bering of Queen's University Belfast ponders some of the more obscure aspects of everyday human behavior. Ever wonder why yawning is contagious, why we point with our index fingers instead of our thumbs or whether being breastfed as an infant influences your sexual preferences as an adult? Get a closer look at the latest data as “Bering in Mind” tackles these and other quirky questions about human nature.