Summary Background The short‐term effect of ambient air pollution on atopic dermatitis (AD), along with its effect modifiers, has not been fully addressed. Objectives To examine the short‐term associations between air pollution and AD, and to identify effect modifications by age and season. Methods We used the generalized additive model to evaluate the short‐term effect of ambient air pollution on daily hospital visits for AD, adjusting for potential confounders. Subgroup analyses were performed to identify potential effect modifications by season and age (< 18 years and ≥ 18 years). Results A total of 29 972 hospital visits for AD were recorded in Guangzhou, China, from 19 January 2013 to 31 December 2017. Among them, 72·8% were visits by children and 51·4% occurred in the cool season. Acute and delayed effects on AD hospital visits were significant for all air pollutants. Stronger effects were seen in the cool season (approximately 1·7–3·0 times higher than effects in the warm season). Stronger effects were also observed in children (approximately 1·3–1·8 times higher than effects in adults). Sensitivity analyses indicated the results were robust. Conclusions Air pollution might be an important trigger for AD in subtropical Guangzhou, China. Children are more vulnerable than adults, and the effects are stronger in the cool season. What is already known about this topic? Atopic dermatitis (AD) has the highest number of disability‐adjusted life‐years among skin disorders. The acute effect of air pollution on AD has not been well studied in China. What does this study add? We found that air pollution (including ambient fine particulate matter, inhalable particles, sulfur dioxide, nitrogen dioxide and ozone) acutely triggers AD, and that children are more sensitive to this effect. The cool season is the vulnerable exposure window for these acute effects.