A developmental map of pathogen-avoidance behaviors

Despite the significant costs of early-life infections, young children show little behavioral avoidance of pathogens. This phenomenon raises still-unanswered questions about when anti-pathogen psychology develops. The present cross-sectional study examined parent-reported observations of 39 behaviors from infancy through middle childhood, based on reports from 3050 parents from the UK and US. Across fine-grained monthly age intervals (0–120 months), distinct developmental trajectories were identified and then grouped into four clusters based on temporal patterns. Behaviors that increased pathogen exposure—such as mouthing and contact with dirty objects—were most frequent during infancy and toddlerhood. Hygiene routines and disgust responses emerged later and remained stable across the observed age range. Two age-related transitions, around the second and fourth years, marked shifts from early exploratory and risk-prone behaviors toward increasingly organized pathogen-avoidant ones. Together, these findings provide a developmental overview of anti-pathogen psychology and clarify when children begin to act in ways that reduce pathogen exposure.