Potential nonmonotonous association between di(2-ethylhexyl) phthalate exposure and atopic dermatitis in Korean children

Summary Background Concerns have emerged about the adverse effect of phthalates on human health. Objectives The aim of this study was to investigate the association between di(2‐ethylhexyl) phthalate (DEHP) exposure and atopic dermatitis (AD) in Korean children, focusing on the potential dose–response relationship. Methods A matched case–control study was conducted from May to October 2012. Subjects from 3 to 6 years of age were recruited from kindergartens and daycare centres in Seoul, Korea. The clinical diagnosis of AD was made by dermatologists. A total of 224 cases and 224 age‐ and sex‐matched controls were included. The levels of two phthalate metabolites [mono(2‐ethyl‐5‐hydrohexyl) phthalate (MEHHP) and mono(2‐ethyl‐5‐oxohexyl) phthalate (MEOHP)] of DEHP in urine samples were measured. Results The effects of DEHP varied by age, and an increased risk for AD was associated with DEHP at age 3 years (odds radio 2·51, 95% confidence interval 1·02–6·20). The association was in the opposite direction in the other age groups although there was no statistical significance. The effects of DEHP on AD was observed differently by the level of the body burden. The predicted risk for AD based on the results of multiple logistic regression analysis showed a nonmonotonous association (U‐shaped) between the level of DEHP and the risk of AD. Conclusions This finding might suggest that the effects of DEHP on AD may be different according to the exposure level or age of the subject. Further longitudinal investigations with a suitable design to investigate the nonmonotonous association should be encouraged. What's already known about this topic? Concerns have emerged about the adverse effect of phthalates on human health. Recent studies have suggested that exposure to phthalates may increase the risk of eczema. What does this study add? The association between the level of di(2‐ethylhexyl) phthalate (DEHP) and atopic dermatitis (AD) was neither linear nor monotonous. This finding might suggest that the effect of DEHP on AD may be different according to the exposure level.