Prenatal and Early-Life Exposure to Indoor Air-Polluting Factors and Allergic Sensitization at 2 Years of Age

To determine the effect of prenatal and early-life exposure to a combination of 7 indoor allergens (air fresheners, candles, mold, cats, dogs, carpet, and environmental tobacco smoke [ETS]) on allergic sensitization at age 2.

This is a secondary analysis of the Kingston Allergy Birth Cohort, from Ontario, Canada, that was established in 2011. Women 18 years or older in the second or third trimester of pregnancy were recruited for the study. A subset of 92 women from the cohort were included in this analysis.

The 92 women included completed prenatal surveys about their environment and surveys at 6 months (n = 76), 1 year (n = 72), and 2 years (n = 81) after the child was born. Questionnaires captured exposure to dogs, cats, mold, carpet, air fresheners, candles, incense and ETS. At 2 years, skin prick testing (SPT) was performed for 14 common food and environmental allergens. Maternal allergic status was also confirmed for 60 of the women via SPT. A positive SPT was defined as a wheal size 3 mm larger than the negative control.

At 2 years, 20 children had a positive SPT. Exposure to cats during the 6-month period (OR 4.267; 95% CI 1.096–15.68), candles during the prenatal period (OR 5.096; 95% CI, 1.697 –13.86) and ETS at 2 years of age (OR 3.78; 95% CI, 1.189–11.18) significantly increased the odds of sensitization. The SPT-positive children had a higher total number of exposures during the prenatal, 6-month, 1- and 2-year period compared with the SPT-negative children (statistically significant difference at all but the 6-month time period). There was a positive trend between number of exposures and positive SPT results for all time points.

The authors found that prenatal exposure to candles, exposure to cats during the 6 month period and ETS at 2 years increased the odds of a positive SPT result at 2 years of age. Prior studies have shown that candles, and phthalates on their own, have been associated with allergic and respiratory disease. This study provides evidence that this exposure may increase the risk of allergic sensitization. Contrary to these results, several studies have found dog and cat exposure to be associated with decreased risk of atopic dermatitis and wheeze or asthma. The authors explain the cat sensitization findings may be due to the age of the children in this analysis (early sensitization may not be lifelong) or cat exposure levels. ETS exposure and risk of atopy have also been reported previously in the literature. In addition, the authors found that children with a positive SPT result at 2 years of age had more exposures prenatally, at 1 and 2 year time points and a dose-response trend was observed. This suggests that multiple exposures may contribute more to allergy development than a single exposure.

This study evaluated the effect of multiple exposures at different time points on odds of sensitization. While this provides valuable information about various environmental risk factors, there are several limitations. The low sample size, especially at the 6-month time frame, makes this study less robust. The authors acknowledge this in their methods, as they were unable to make corrections for multiple comparisons due to the small sample size. Therefore, it is unclear if confounding impacted the identified relationship. In addition, the information on environment was collected via questionnaire instead of using samples from the home. Finally, sensitization does not always equate to clinical allergy. This study has identified several exposures, candles, cats, and ETS, that warrant further evaluation. A larger study with better environmental exposure and allergic sensitization and outcome measurements is needed.