Most people attribute Northern Ireland’s repeated rejections of same-sex marriage to its strong Catholic tradition and conservative values. But could the real culprit be sewage problems or air pollution?

A team of psychologists and political scientists from the University of Arkansas have found that people are less likely to support gay marriage if they’re in an odorous environment. For a study whose results were published this month in the journal PLOS ONE, political science professor Patrick Stewart and his colleagues recruited 57 participants and assigned them to take questionnaires on their social and political views in either an odorless room or a disgusting-smelling one. For the unlucky volunteers assigned to the “disgusting odor” group, the researchers added drops of butyric acid—the chemical best known for giving human vomit its smell—on cotton pads and hid them around the room.

Participants in the disgusting condition were far less tolerant of gay marriage and even gay relationships:

They also took a more conservative stance toward premarital sex, pornography, and abortion. Older participants’ views were particularly affected by the foul smell. “It is possible,” the authors hypothesize, “that exposure to a disgusting odorant caused increased feelings of disgust, which in turn activated the harm avoidance system and motivated a desire for purity (cleanliness).” If all those arguments about love and equality aren’t convincing people, maybe gay rights activists should focus on perfuming the air around voting booths.