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.