Asthma is a respiratory disease that can be exacerbated by certain environmental factors. Both formaldehyde (FA) and PM2.5, the most common indoor and outdoor air pollutants in mainland China, are closely associated with the onset and development of asthma. To date, however, there is very little report available on whether there is an exacerbating effect of combined exposure to FA and PM2.5 at ambient concentrations. In this study, asthmatic mice were exposed to 1 mg/m3 FA, 1 mg/kg PM2.5, or a combination of 0.5 mg/m3 FA and 0.5 mg/kg PM2.5, re...