Purpose: There is a lack of a report about the trajectories of allergen sensitization, although it is important to understand the change of allergen sensitization to manage allergic disease. This study aimed to analyze the change and trajectories of allergen sensitization in children with respiratory and allergic diseases. Methods: From 2006 to 2020, children with respiratory and allergic diseases or screened for allergic sensitization were evaluated. We visualized the alterations and the trajectories of allergen sensitization using stacked area graphs, box plots, and Sankey diagrams. Results: A total of 2,804 subjects were included, and allergic rhino-conjunctivitis was diagnosed in 1,931 children (68.9%). The mean age for the first test was 4.1 years, and that for the second test was 6.5 years. Children sensitized to class 1 food allergen before age 5 showed sensitizations more for other allergens and at a younger age after age 5 than children who were not. The atopic tendency continued once it had been obtained before the early school age in the persistence or the new development of sensitization. Conclusion: Allergen sensitization has changed over time and has shown different patterns according to age. Its trajectory has taken a wide variety of courses in children with respiratory and allergic diseases until the early school age. These changes reflect the allergic diseases and socio-environmental characteristics of children and adolescents. (Allergy Asthma Respir Dis 2023;11:34-42)