The present study has some limitations. An obvious limitation is that we detected the pyrethroid metabolites with only one spot urine sample, which might not fully reflect the long-term exposure. Sequential measurements would obtain a more accurate and comprehensive evaluation of exposure levels. Pyrethroids are metabolized rapidly in the human body, which makes it difficult to reflect chronic or intermittent exposure in metabolites (Berkowitz et al., 2003). Also, children's age had a wide range in this study, which could increase the heterogeneity of the CBT cases, because the pathological development of the disease might be different among infants, young children, and adolescents.