It’s no secret that when traveling abroad, people often find local residents’ body odor particularly offensive. And mothers tend to believe that other infants smell far less appealing than their own. Now, in a study published this week in Proceedings of the National Academy of Sciences, a group of researchers has shown that the degree of disgust people find in others’ sweat may vary with group identification. In other words, disgust may depend on whether one considers the person they smell to be a member of their “in-group” or “out-group.”

The researchers performed two sets of experiments: In the first they asked 45 female University of Sussex students to hold and smell a sweaty T-shirt bearing the logo of another university and report how disgusting they found it on a scale of 1 to 7. The students believed they were participating in an experiment measuring their ability to detect pheromones. The researchers then subtly primed the students to think of themselves as members of different groups or no group at all by telling them different versions of the study’s purported goals. In some cases the researchers said they were measuring how well students could detect pheromones—activating the study subjects’ feelings of affiliation with all other students, including those at the university printed on the T-shirt. Other times the researchers said they were testing the detection ability of Sussex students, priming the study participants to think of the T-shirt as having belonged to a member of a rival group. As a control condition, the researchers said they were looking at individual ability.

The researchers found that the students were considerably less disgusted when they considered the T-shirt’s source a member of the same group (a fellow student) compared with a member of a different group (a student at a rival university) or when they were not thinking of groups at all. Because the students felt the same amount of disgust when they perceived the T-shirt as having belonged to an “outsider” and when they were not thinking about groups at all, the researchers concluded that feelings of in-group affiliation reduced feelings of disgust. In other words, regarding someone as an “other” does not necessarily increase revulsion but the idea that he or she is “one of us” may decrease it.

The second experiment involved giving 90 male and female University of Saint Andrew’s students sweaty T-shirts with either a Saint Andrew’s logo, that of a rival university or no logo at all. Then the researchers recorded how quickly the students walked across the room to a hand sanitizer station and how many pumps of sanitizer they used after handling the sweaty shirt. The researchers observed the same patterns as before: When the T-shirt belonged to someone in the same group, the students moved less quickly across the room and used less hand sanitizer.

Scientists have linked the emotion of disgust to an evolutionary instinct to avoid pathogens and protect against infection. As such, disgust is thought to mediate relations between groups—in other words, it plays an important role in keeping people apart from out-groups who might harbor unfamiliar and potentially dangerous germs. The new study adds a new element to that idea, says John Drury, a psychologist at Sussex and one of the study’s authors. “It also helps socially to reduce the level of disgust—in order to work together and do things as a group, since a lot of things in society are achieved in groups.”

Jolanda Jetten, a psychologist at The University of Queensland who was not affiliated with this work, notes previous studies have shown people are very tolerant of unpleasant odors and even waste products when dealing with their children or an intimate partner. This research builds on those findings by demonstrating that not only intimacy but shared identification is important in conditioning disgust. “It shows that even something as basic as smell is regulated by group processes,” she says.

These findings may help social scientists explain how different groups cooperate, extending to research on racism and dehumanization. “This [study] suggests that it is possible to overcome feelings of disgust by changing the relationship between the disgusted and the disgusting,” says Alex Haslam*, also a psychologist at Queensland who did not participate in this study. “I think this is very neat research that makes a very powerful point in an ingenious and compelling way.”

According to Stephen Reicher*, a psychologist at Saint Andrew’s and the study’s lead author, the team plans to continue this research by studying how reduced levels of disgust in an ingroup mediates both physical and mental cooperation, generalizing these findings across larger, real-world settings. The researchers may test different identities, beyond that of “student” and use stimuli other than sweaty T-shirts, perhaps involving taste or even socioeconomic preferences instead of odor. “But we also want to look at some of the paradoxes and downsides of lowered in-group disgust,” Reicher adds. “The lowering of disgust may lead people to lower their guard in practices that contribute to spreading infection—more willingness to share food and drink, to stay near ill people and not turn away if they cough, and so on.” The implications are international in scope. “At the Hajj, for instance, people come from 162 nations, mingle their germs and go back home to spread them further. We are interested in the psychological dimension of this process,” he says.

*Editor’s Note: Both Haslam and Reicher are members of Scientific American MIND’s Board of Advisers