Contagion in Relationships: Can You "Catch" Infidelity?

While psychologists often focus on the individual as their unit of analysis, no individual has ever existed in perfect isolation from others, at least not for long. Like ants, people interact throughout their lives, creating “emergent organizations at a higher level than the individual.”

As Robert Goldstone (Indiana University) and Marco Janssen (Arizona State University) note: “The emergence of higher-level organizations from the interactions of lower-level units is surprising in the case of group behavior because we are the lower-level units, and the higher-level organizations typically emerge spontaneously, without our knowledge. Social phenomena such as rumors, the emergence of a standard currency, transport systems, the World Wide Web, resource harvesting, crowds, and scientific establishments arise because of individuals' beliefs and goals, but the eventual form that these phenomena take is rarely dictated by any individual.”

These emergent properties of social existence are facilitated in large part by what psychologists call social contagion. Defined as “behavior, emotions, or conditions spreading spontaneously through a group or network,” contagion effects have been demonstrated across a wide range of phenomena including obesity, sleep patterns, smoking, alcohol abuse, marijuana use, loneliness, happiness, depression, and cooperation, among others.

Social contagion manifests mainly in two ways: how we feel (emotional contagion) and how we act (behavioral contagion). Research has shown people's propensity for emotional contagion. Our facial expressions and movements tend to increasingly coordinate in a crowd using facial, vocal, and postural mimicry. In effect, we tend to “catch” other people’s emotions. “As a response to emotional contagion,” write Dutch psychologists Carolina Herrando and Efthymios Constantinides, “individuals show behavioral, attentional, and emotional synchrony.” You are unlikely to be happy in a room full of sad people.

Behavioral contagion involves the spread of behavior through a group. The term, which appears to have originated in the mid-1890s to explain crowd behavior, refers to our tendency to copy or mimic the behavior of proximate others. You can see contagion effects around you in many situations. For example, “audience members who all applaud or rise to a standing ovation after an initial person does, regardless of whether they actually enjoyed the performance, are demonstrating behavioral contagion.” Varied behaviors such as risk-taking, laughter, rudeness at work, and self-disclosure norms have all been shown to be under contagion influence.

Social contagion research has also looked into the role of contagion in affecting our sexual behaviors and intimate relationships. Contagion has been shown to play a role in adolescent promiscuity. Divorce has been shown to be contagious. Some have argued that recent increases in reports of gender dysphoria are the result of contagion.

A recent paper (2022) by Israeli researcher Gurit Birnbaum and colleagues, has sought to examine social contagion processes around infidelity. Birnbaum’s team conducted three separate studies, to see whether "online exposure to norms of adultery would affect perceptions of the current relationship and expressions of desire for alternative mates.” In all studies, “partnered participants were exposed to other people’s cheating behavior and then thought of attractive strangers or actually encountered them. Their relationship perceptions and reactions during these experiences were recorded.”

Specifically, in Study 1, 145 (partnered) undergraduate students were randomly assigned to watch a video that presented research that indicated either high or low prevalence of infidelity. Participants were then asked to describe an extra-dyadic sexual fantasy narratively. Independent judges coded these fantasies for expressions of sexual desire for current and alternative partners. The results, however, fail to support the contagion hypothesis as “the manipulation of prevalence of infidelity did not significantly affect participants’ sexual desire for both current and alternative partners, at least as manifested in their fantasies.”

Study 2 exposed 132 partnered participants to incidents of cheating on either one’s current partner or academic work. Participants then viewed photos of strangers of the opposite sex and indicated their willingness to consider the pictured individual as a potential partner. The number of selected partners was taken to represent their levels of interest in extra dyadic targets. The results of this study did support the contagion hypothesis "indicating that exposure to norms of adultery (rather than the mere general exposure to cheating in non-sexual domain) increases people's likelihood of considering attractive others as potential partners."

Study 3, explored whether exposure to adultery norms would increase not only infidelity desire, but the effort toward fulfilling that desire. Based on previous findings, the authors predicted that exposure to adultery norms would increase expressions of desire for alternative mates, which, in turn, would be associated with greater efforts made to interact with them in the future. In the study, 140 participants were first exposed to norms of either adultery or cheating in academics. Then, they were interviewed, using an online platform, by an attractive interviewer of the opposite sex. At the interview’s end, participants were “asked to leave one last message for the interviewers.” These messages were then coded for whether they contained efforts to solicit future interactions. Participants also rated the interviewer’s sexual desirability, as well as their own commitment to their current partner. The results here were mixed. “The findings showed that compared to exposure to norms of cheating in academics, exposure to adultery norms decreased commitment to the current partner, but did not significantly affect expressions of desire for alternative partners."

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The researchers interpret their results overall as showing that “following exposure to others’ cheating behavior, participants were less likely to devalue the attractiveness of alternative partners and to be committed to their relationship. These findings suggest that exposure to adultery norms decreases the awareness of long-term priorities of relationship maintenance, lessening the resistance to the temptation of attractive alternatives.”

Birnbaum's work here should be interpreted with caution. For one, the results were mostly mixed with regard to the power of contagion in this context. Moreover, the contagion manipulations used were weak (e.g., reading a paragraph about cheating), which means that existing effects may not have been detected and that the detected effects may have been due to mere priming, rather than contagion. But the overall findings align with the diverse literature suggesting strongly that, because of our tendency toward social contagion, the control of our behavior, as much as we Americans dislike acknowledging it, is situated largely outside of us. As the old Yiddish saying goes: “The mouse isn’t the thief, the hole in the fence is the thief.”

One important implication of this emerging understanding is that expecting people to stay on the path of behavioral and emotional goodness solely by their individual will, commitments, and values is naïve, even dangerous. This is because, for human beings, survival and individual thriving depend entirely on group support. Our deepest impulses, therefore, are to go along with the group. In a bad group, most people, even the good ones like you, will end up behaving badly.