Indoor formaldehyde exposure and asthma in adults : a systematic review

Abstract

Introduction Due to its widespread use, toxicity and volatility, exposure to the chemical formaldehyde has important implications for human health. Asthma is a common chronic inflammatory disease with both genetic and environmental factors. The common symptoms of asthma include wheezing, coughing, and shortness of breath. The objective of the present study is to evaluate the association between exposure to formaldehyde and adult asthma through systematic review.

Methods A literature search was conducted using PubMed with keywords of formaldehyde, adult asthma, and other relevant terms.

The basic exclusion and inclusion criteria in this study are as follows:

Original randomized controlled trials (RCTs) and observational studies were eligible, but not editorials, reviews, case-reports and case‐series. Studies that focused on behavioral change or other outcomes unrelated to asthma were excluded. Lastly, articles in which full text was unavailable were excluded.

Finally, after 3 selection rounds, 7 studies were included in the present systematic review.

Results: These 7 studies included 3 RCTs, 2 case‐control studies and 2 cross‐sectional studies, published from 1986 to 2013. The 3 RCTs examined participants with and without asthma and investigated the acute effects of formaldehyde on respiratory phenotypes; in contrast, the 4 observational studies examined the long‐term effects of low dose formaldehyde exposure on asthma.

Only 1 RCT reported a strong association between formaldehyde and adult asthma, with the intervention group developed an immediate bronchial response at a significantly lower dose of mite allergen than that of the control group with air exposure. The other 2 RCTs found no significant deleterious effect on airway allergen responses after exposure to 500 μg/m3 formaldehyde; and the concentration of formaldehyde found in the indoor environment was of minor importance for developing pulmonary symptoms.

Two case-control studies reported a positive association between formaldehyde exposure and asthma symptoms, while the results in the cross‐sectional studies suggested no significant association between formaldehyde exposure and adult asthma.

Conclusions Among the 3 reviewed RCTs, only 1 reported a significant association between formaldehyde and asthma. In the 4 reviewed case‐control and cross‐sectional studies, 2 suggested that exposure to formaldehyde had significant effects on bronchial responses. However, these studies represented different characteristics, hence, after integration of them, this review suggests that exposure to formaldehyde in relative low concentration may not have strong association with adult asthma. However, further studies are required to A: Try to identify more potential confounders and choose most suitable model in various conditions; B: investigate multiple patterns of formaldehyde exposure and provide different outcome measurements in RCTs. In addition, this report indicates that it is important to increase the population awareness of choosing environmental friendly decoration materials for reducing formaldehyde exposure.