Background: The early life microbiome can shape human immunity. Recent studies have revealed gut dysbiosis after laxative administration. Objective: To investigate the impact of infantile laxative exposure on subsequent allergic diseases. Methods: This nationwide matched cohort study was conducted using Taiwan's National Health Insurance Research Database for the period 1997 to 2013. A total of 32,986 patients who had complete information of maternal history and delivery modes were identified. We included 291 children having laxatives for at least 7 days within the first 6 months of life and 1164 reference children not receiving laxatives, matching by sex, propensity score, number of hospital visits, and maternal age at delivery. Demographic characteristics and maternal factors were compared, and cumulative incidences of allergic diseases were calculated. Cox proportional hazard model was used to evaluate associations. Results: The 5-year cumulative incidence of allergic diseases in the laxative cohort was significantly higher than that in the reference cohort (49.81% vs 41.68%; P =.01). Early life laxative exposure (adjusted hazard ratio, 1.61; 95% confidence interval, 1.32-1.97) was independently associated with allergic disease development. Other independent risk factors included preterm, male sex, maternal allergic diseases, and prenatal laxative use. Multivariable stratified analyses verified the association between early life laxative exposure and subsequent allergic disease development in all subgroups of children, including those born to mothers without allergic diseases or prenatal laxative use. Conclusion: Early life laxative exposure is associated with allergic disease development.