Introduction: It has not been well investigated how atopic dermatitis (AD) flares are affected by weather and air pollution. This study aimed to investigate how the effects of particulate matters ( PMs) on AD symptoms are influenced by weather. Methods: A total of 125 young children with AD under 6 years of age living in Seoul, Korea, were enrolled as a panel and followed for 17 months between August 2013 and December 2014. AD symptoms including itching, sleep disturbance, erythema, dry skin, oozing, and edema were recorded on a daily basis. Daily weather was classified into 7 categories according to Spatial Synoptic Classification (SSC): dry moderate (DM), dry polar (DP), dry tropical (DT), moist moderate (MM), moist polar (MP), moist tropical (MT), and transition. Personal exposure to particles with an aerodynamic diameter less than 2.5 ( PM2.5) and 10 μm ( PM10) in each individual was estimated with time-weighted average of concentrations considering outdoor and indoor level of PMs and time activity of each individual. To analyze the effects of PM2.5 and PM10 on AD symptoms, a generalized linear mixed model (GLMM) was used controlling for ambient temperature and humidity, age, sex, SCORAD at enrollment, fever, day of week, and topical steroid treatment. Results: A total of 22,221 person-days of symptom records were collected. The presence of AD symptoms was higher on cold dry (DP) days (45.0%, P .0001) and lower on hot humid (MT) days (36.2%, P .0001). Overall, the risk of AD symptoms significantly increased by the exposure to PM2.5 and PM10 [adjusted odds ratio (aOR) = 1.063 (95% confidence interval (CI), 1.016-1.113) and 1.034 (95% CI, 1.012-1.056) per 10 μg/m3, respectively]. Among 7 weather types, the risk of AD symptom caused by exposure to PM2.5 was significantly increased only on DM days (aOR = 1.135; 95% CI, 1.063-1.213), while those to PM10 were significantly increased on DM days (aOR = 1.070; 95% CI, 1.034-1.108), MM days (aOR = 1.066; 95% CI, 1.011-1.124), and MT days (aOR = 1.083; 95% CI, 1.010-1.161). Interestingly, the adverse effects of PM2.5 were higher than PM10 for all weather types. Conclusion: The detrimental effects of PM10 and PM2.5 on AD symptoms vary by weather types and are enhanced under specific weather types. Weather type should be considered to evaluate the effect of air pollution on AD symptoms.