This study investigated the individual and social determinants of the public’s phobia of infectious diseases in South Korea, where collective action was recently fueled by the public phobia over mad cow disease (bovine spongiform encephalopathy [BSE]). Gender-specific multivariate regression was used to compare the public perception of BSE and highly pathogenic avian influenza (HPAI). The analysis results differentiated between the determinants of the phobia for the 2 diseases, BSE and HPAI (N = 1002). As with HIV/AIDS and leprosy, the public fear of HPAI was expressed as a disease phobia that seeks to ensure the social exclusion of infection sources, whereas the fear of BSE was influenced by social and communication factors. Therefore, BSE, unlike previous HPAI, can be rapidly amplified amid the growing distrust in health communication, in which case the social determinants of disease phobia are associated with communicator trust, social values, and political attitude toward diseases rather than disease perception.