Effect of Formaldehyde on Asthmatic Response to Inhaled Allergen Challenge

Background: Exposure to formaldehyde may lead to exacerbation of asthma. Objectives: Our aim in this study was to investigate whether exposure to a low level ($500 \mu g/m^3$) of formaldehyde enhances inhaled allergen responses. Methods: Twelve subjects with intermittent asthma and allergy to pollen were exposed, at rest, in a double-blind crossover study to either formaldehyde or purified air for 60 min. The order of exposure to formaldehyde and air-only was randomized, and exposures were separated by 2 weeks. We also performed an allergen inhalation challenge after each exposure. Airway responsiveness to methacholine and lower airway inflammation (induced sputum) were assessed 8 hr after allergen challenge. Results: The median dose of allergen producing a 15% decrease in forced expiratory volume in 1 sec ($PD_{15}FEV_1$) was 0.80 IR (index of reactivity) after formaldehyde exposure compared with 0.25 IR after air-only exposure (p = 0.06). Formaldehyde exposure did not affect allergen-induced increase in responsiveness to methacholine (p = 0.42). We found no formaldehyde-associated effect on the airway inflammatory response, in particular the eosinophilic inflammatory response, induced by the allergen challenge 8 hr before. Conclusion: In this study, exposure to$500 \mu g/m^3$formaldehyde had no significant deleterious effect on airway allergen responsiveness of patients with intermittent asthma; we found a trend toward a protective effect.