[Clinical aspects of occupational asthma].

Although on the increase overall, the actual prevalence of occupational asthma is difficult to assess because of variations seen according to periods, countries, jobs, and the agents responsible. In the authors' experience, this prevalence is slightly less than 10%. Three principal mechanisms, sometimes present together, not always elucidated: immunological, reflex and irritative, are responsible for such asthma. Whilst a positive diagnosis raises few problems, the aetiological diagnosis is difficult and involves two stages: recognition of the occupational characteristic of the asthma and attribution of this asthma to an allergen or substance in the occupational environment. Skin tests and in vitro tests, but above all exposure tests, make an important diagnostic contribution. Personal examples are used to illustrate the principal aetiological factors in occupational asthma of animal, vegetable or chemical origin.