There is a long and sometimes ignoble history of occupational diseases being normalised and/or wrongly attributed to factors outside the workplace. In 1919, for example, a local physician blamed the “black lung” of Appalachian coal miners on “housing conditions and hurtful forms of recreation”.1 Sixteen years later the disease was still considered “an ordinary condition that need cause no worry”.2 When occupational diseases are considered “natural”, or are ascribed to characteristics of the worker or his domestic environment, then there is little incentive to improve working conditions.

The last decade or so has seen a paradigm shift in our understanding of occupational asthma. It is no longer considered a disease that solely reflects individual susceptibility; there is now a consistent body of evidence relating its incidence—at least at a population level—to the intensity of allergen exposure in the workplace. Thus, even if the details of exposure-response relations and their thresholds (if any) remain hazy, it has become an …