Numerous risk factors are associated with asthma. To achieve adequate precision in epidemiologic studies of asthma, large populations and specific diagnostic methods are to be preferred. The association between air pollution (in a wide sense) and adult-onset asthma is well-known, but little is known about the actual risks. In published studies the fraction of adult-onset asthma caused by occupational exposures ranges from 4.8% to 36%. Whether subjects with preexisting asthma are at an increased risk for impairment due to asthma when they are exposed to irritants is an issue of great relevance. The literature addressing these problems is scant. The challenge facing us is to design epidemiologic studies on adult asthma that lead to answers to the following questions: (i) has the incidence of asthma increased among adults, (ii) to what extent is adult-onset asthma caused by occupational exposure, (iii) does preexisting asthma get worse due to exposures in the workplace?

Key terms exacerbation; incidence; natural history; occupational exposure