To bae or not to bae? That is the question of dating. And while you might believe the answer hinges mostly on "chemistry" or mutual interests, a team of psychology researchers from McGill University in Montreal suggests that there's an unlikely judge ultimately making the call: your behavioral immune system.
Unlike your physiological immune system — that collection of cells, organs and lymph nodes that defends your body from invading pathogens and sweeps up the microscopic debris cluttering your tissues — your behavioral immune system relies on subconscious sensory impulses to steer you away from potential germ-ridden danger. (While the concept of a second immune system is only about 10 years old, the notion that humans and other animals noticeably change their behavior to avoid communicable diseases has been demonstrated in hundreds of studies.) This system may be the reason you feel compelled to switch bus seats when the person sitting next to you is constantly hacking up phlegm, why you feel disgusted by certain smells and why you balk at pimple-popping videos on YouTube.
Your reactions to gross stimuli like these can prime your white blood cells for action. And this immune response may also ruin your hot date, according to the researcher's study in February 2018 issue of the journal Personality and Social Psychology Bulletin.
"We found that when the behavioral immune system was activated, it seemed to put the brakes on our drive to connect with our peers socially," study author Natsumi Sawada, a psychologist and former student at McGill University, said in a statement.
In the study, Sawada and her colleagues recruited several hundred people ages 18 to 35, who were single and heterosexual, to participate in either an in-person or online speed-dating experiment. Before the dating events began, each participant answered a questionnaire to measure what the researchers called "perceived vulnerability to disease" (PVD) — basically, how germ- and disease-conscious the person was. (Sample prompt: "I avoid using public telephones because of the risk that I may catch something from a previous user.")
Next, participants either sat down for a 20-minute conversation with an attractive student, ran a gauntlet of 3-minute speed dates or rated a series of online dating profiles custom-made for the study. After each dating encounter, the singles rated their potential partner's attractiveness, "dateability," and how friendly or withdrawn they seemed. Across every trial, daters who were more concerned with germs and infection (measured by higher PVD scores) were consistently rated as less friendly than daters who weren't. Germophobes also reported feeling less romantic interest in their partners than the less-finicky participants did.
To make sure this correlation was more than a coincidence, the researchers ran a final speed-dating experiment in which half of the participants first watched a 2-minute video called "Top 10 Revolting Hygiene Facts," while the other half watched a control video about words with no English equivalents. During the following speed-dating game, participants primed with the gross-out video reported "significantly less romantic interest" than the control group did, according to the study.
"The results suggest that, beyond how we consciously or unconsciously think and feel about each other, there are additional factors that we may not be consciously aware of — such as a fear of disease — that may influence how we connect with others," Sawada said.
If this resonates with your own love life, consider that kissing itself may have evolved as an immunological tool. Every time you swap saliva, you also swap pheromones, hormones and millions of bacteria that may contain important genetic information about your partner. Whether you'd prefer to learn that information this way is up to you — and your immune system, of course.