Objectives: The aim of this study was to determine the lag between exposure to air pollutants and changes in human eosinophil counts. Material and Methods: This was a retrospective study employing 246 425 physical examination records dated December 2013 – December 2016 from Chengdu, China. The authors determined the prevalence of individuals with eosinophil counts above the normal reference range each day. A distributed lag non-linear model was used to evaluate the lagged effect of each air pollutant on eosinophil counts. The lagged effects of each air pollutant were counted and presented with smoothing splines. Results: The effects of air pollutants such as particulate matter (PM_2.5, aerodynamic diameters <2.5 μm; PM₁₀, aerodynamic diameters <10 μm), nitrogen dioxide (NO₂) and ozone (O₃) were evaluated. In women, the effects of PM_2.5 (RR = 1.154, 95% CI: 1.061–1.255) and PM₁₀ (RR = 1.309, 95% CI: 1.130–1.517) reached the maximum values on lag day 0. In men, there was no significant effect of PM_2.5, but significant effects of PM₁₀ were found for lag days 20–28. The effects of NO₂ and O₃ on eosinophils were not statistically significant for either gender. Conclusions: The air pollutants of PM₁₀ have a significant effect on human eosinophils for both women and men, but with different temporal patterns, with women showing a lag of 0–5 days and men showing a lag of 20–28 days. In addition, PM_2.5 was significant for women with a lag of 0–3 days but it was not significant for men. Int J Occup Med Environ Health. 2020;33(3):299–310