Are asthmatics more sensitive to irritants?

Asthma is a heterogeneous inflammatory disease characterized by increased airway hyper-responsiveness to external stimuli such as irritants. One may speculate that asthmatics are more sensitive to irritants in the air than healthy subjects, i.e. react at lower concentrations. We reviewed the scientific support for this speculation and investigated to what extent asthma is considered when setting exposure limits and guidance values. We found that the experimental studies comparing healthy and asthmatic subjects are often inconclusive. Still, the available studies are underused, by expert committees and industry alike. Data for a few irritants suggest that asthmatics are up to three-fold more sensitive than the healthy. The most abundant data were found for sulfur dioxide. Here, a benchmark concentration analysis suggests a nine-fold difference in sensitivity. Based on these data a default assessment factor of 10 is suggested when setting exposure limits and guidance values for irritants.