It's no secret that when abroad, travelers often find local residents' body odor particularly noxious. Now a study published in March in the Proceedings of the National Academy of Sciences USA shows that the degree of disgust we find in others' sweat may depend on whether we are thinking of them as part of our social group or as outsiders.

The team—led by Stephen D. Reicher, a psychologist at the University of St. Andrews (and a member of Mind's advisory board)—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. They subtly primed the students to think of themselves as members of different groups 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 the implied owner of the sweaty T-shirt. Other times the researchers said they were testing the detection ability of Sussex students, priming the study participants to think of the non-Sussex tee as having belonged to a member of a rival group. As a control condition, the researchers said they were looking at individual ability.

The students were considerably less disgusted when they thought the T-shirt's owner was in their group (a student at any university) compared with a different group (a student at a rival university) or when they were not thinking of groups at all. The researchers concluded that regarding someone as an “other” does not necessarily increase revulsion, but the idea that he or she is “one of us” may decrease it.

In a second experiment, 90 male and female St. Andrews students handled sweaty T-shirts with either a St. Andrews logo, that of a rival university or no logo. The researchers noted a similar effect: when the T-shirt seemed to be of their own group, the students moved less quickly across the room to a hand sanitizer station and used fewer pumps.

Scientists have linked disgust to an evolutionary instinct to avoid pathogens—from rotting meat or fouled water, for example. It also may keep us wary of strangers who could harbor unfamiliar germs. The new study adds an element to previous work confirming that people are remarkably tolerant of bad odors and even waste products when dealing with loved ones, says Jolanda Jetten, a psychologist at the University of Queensland in Australia, who was not involved in the study. “It shows that even something as basic as smell is regulated by group processes.”