Children who are exposed to ozone (O3) and nitrogen dioxide (NO2) air pollutants at birth and during early life may have an increased risk for incident asthma and eczema compared with children not exposed to these oxidant pollutants, study results published in the European Respiratory Journal suggest.

A total of 1286 participants in the Toronto Child Health Evaluation Questionnaire (T-CHEQ) study were included in the analysis. Participants were followed from birth until the incidence of asthma, eczema, or allergic rhinitis, or until March 31, 2016, or loss to follow-up (mean follow-up duration, 17 years). Incident asthma, eczema, and allergic rhinitis diagnoses were identified using International Classification of Diseases codes, and the Ontario Registered Persons Database was used to identify participants’ air pollution exposures by postal codes at birth.

In the T-CHEQ follow-up cohort, approximately 28.5% (n=366) had asthma, 39.7% (n=511) had allergic rhinitis, and 74.5% (n=958) had eczema. Of the whole cohort, 14% (n=177) had all 3 conditions.

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Children who were exposed to O3 at birth had a 1.2-fold higher risk for asthma (hazard ratio [HR], 1.22; 95% CI, 1.04-1.43) and allergic rhinitis (HR, 1.15; 95% CI, 1.00-1.31) per interquartile range in an adjusted analysis. In the multipollutant model, exposure to NO2 at birth was most strongly associated with both asthma (HR, 1.17; 95% CI, 1.05-1.31) and eczema (HR, 1.07; 95% CI, 0.99-1.15). Taken together, exposure to NO2 and O3 increased the risk for asthma and eczema.

A limitation of the study was the estimation of air pollution exposure by place of birth and residence, which could have overestimated or underestimated exposures.

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On the basis of the findings, the researchers suggested that improving air quality and “reducing air pollution exposure especially to O3 and NO2 may contribute to the prevention of asthma and other allergic disease in childhood and adolescence.”


To T, Zhu J, Stieb D, et al. Early life exposure to air pollution and incidence of childhood asthma, allergic rhinitis and eczema [published online December 5, 2019]. Eur Respir J. doi:10.1183/13993003.00913-2019