The decrease of symptomatic atopic isocyanate workers over time is remarkable and could be due to the following reasons: i) the negative selection of the atopics (e.g. on the basis of an earlier development of non-IgE-mediated isocyanate asthma in atopics), ii) a protective effect of longer isocyanate exposure upon the development of atopy. Here, IGHE is linked to asthma.