Background <p>Public health emergencies have been found to be significantly associated with mental health outcomes, yet their association with suicidal ideation remains insufficiently explored. The present study aimed to examine the cross-sectional association between public health emergencies and suicidal ideation among college students, with a particular focus on the potential mediating role of fear of missing out (FoMO) and the moderating role of conscientiousness.</p> Methods <p>A cross-sectional survey was conducted among 1,012 college students from a university in Guangdong Province, China. Participants completed questionnaires assessing exposure to information about public health emergencies, FoMO, suicidal ideation, and the Big Five Personality Traits Inventory. The PROCESS macro in SPSS was used to test the mediation and moderation effects.</p> Results <p>The results revealed that (1) public health emergencies were positively associated with suicidal ideation; (2) FoMO mediated the relationship between public health emergencies and suicidal ideation; and (3) The moderating effect of conscientiousness was significant, such that the positive association between public health emergencies and FoMO was stronger at higher levels of conscientiousness, whereas the positive association between FoMO and suicidal ideation was weaker at higher levels of conscientiousness.</p> Conclusions <p>These findings suggest that public health emergencies and suicidal ideation are associated through FoMO. Conscientiousness exhibits a two-stage moderating effect in the pathways from public health emergencies to FoMO and subsequently from FoMO to suicidal ideation. The study highlights that addressing FoMO is associated with lower levels of suicidal ideation among college students, and suggests integrating conscientiousness into mental health interventions during public health emergencies. Future longitudinal or experimental research is needed to establish causal directions.</p>