Infection changes social orientations: The effect of disease salience on shifts in individualism and collectivism

Collectivism and individualism are key indicators of social orientation changes under the threat of infectious diseases. Although previous studies have identified indirect relationships between infectious diseases and collectivism, none have directly tested causality. We used visual stimuli to heighten disease salience and directly tested whether collectivism and individualism changed before and after exposure among Japanese participants. In Study 1, the intervention was divided into two main conditions: infectious disease-related threats and non-related threats. In Study 2, disgust and fear—key factors in responses to disease threats—were isolated into four distinct conditions. The results showed that visual stimulation effectively heightened disease salience, leading to changes in collectivism and individualism. However, contrary to existing hypotheses suggesting an increase in collectivism, we consistently observed an increase in horizontal individualism. This study is the first to demonstrate a causal relationship between infectious disease threats and social orientations, while potentially suggesting that these threats drive a shift toward horizontal individualism rather than collectivism. • Infection-related visual cues activate the behavioral immune system via germ aversion. • Both infection and general threats shift social orientations, not just infection cues. • Horizontal individualism increases after exposure to disgust–fear combined stimuli. • Disgust alone increases vertical individualism; fear alone shows no significant effect. • Behavioral immune system activation causally alters social orientation.