Beyond the Ewwwww: Micro-level Interpersonal Motives and the Dual Dynamics of Behavioral Immunity
Classic accounts characterize the behavioral immune system (BIS) as a set of psychological processes guiding contact and social decisions to reduce behavioral exposure to pathogens, yet real-world evidence challenges several of its core predictions. Across longitudinal studies during the COVID-19 pandemic and a cross-cultural registered report, we found little evidence that ecological disease salience or ethnic outgroup cues—two factors often cited as important influences—reliably increased avoidance or xenophobia. This raises a broader question: if abstract macro-level cues are insufficient, what actually regulates disease-related behavior? Our work suggests that the answer lies in micro-level interpersonal motives. People are more willing to risk infection with close or valued partners, and less willing with untrustworthy or low-value ones. Longitudinal data likewise show that people’s evaluations of their interaction partners, and their comfort with microbe-sharing contact, depend more on partner identity than on epidemic curves. Crucially, this tuning is not limited to healthy perceivers. Infected individuals also adjust: with high-value partners, they conceal illness less and sometimes even disclose it more. Together, these findings reveal that pathogen regulation is inherently relational and dynamic, shaped by motives such as avoiding infection, preventing exploitation, reducing social exclusion, and seeking care. Importantly, they highlight that contagion is a two-sided interaction: healthy individuals regulate avoidance, while infected individuals regulate disclosure, each negotiating social value in different ways. This dual perspective not only reframes behavioral immunity as a socially embedded motivational system, but also points toward the need to integrate BIS with physiological immunity (PIS). Our future work takes this step by examining gut–brain pathways as one entry point into how biological states and social motives jointly shape disease behavior and interaction.