Protective but Costly: The Impact of Behavioral Immune System Reactivity on Mental Health

The behavioral immune system (BIS) refers to a set of evolved psychological mechanisms designed to detect cues of potential pathogen threat and trigger self-protective, avoidant behaviors. However, like all adaptations, the BIS carries potential costs alongside its benefits. This study aimed to examine the impact of BIS-related processes on mental health outcomes—including depression, anxiety, stress, and obsessive–compulsive symptomatology—during the COVID-19 pandemic. Data were collected online at two time points: the onset of the pandemic (May 2020; n = 990; 86% women) and at the end of its first year (November/December 2020; a subsample of the original participants, n = 182). Hierarchical regression analyses were conducted, entering socioeconomic variables and general quality of life in the first block, followed by BIS-related variables (germ aversion and perceived infectability) in the second block. Results showed that socioeconomic status and general quality of life were significant predictors of mental health difficulties at both time points, consistent with prior findings on the harmful effects of environmental and social stressors. Importantly, BIS variables also emerged as significant and independent predictors of mental health outcomes—including the development of obsessive–compulsive symptoms—highlighting the potential psychological costs of pathogen-avoidant motivations governed by the BIS.