Occupational asthma is defined as a form of asthma that is generally caused by immunological sensitization to a (specific) agent inhaled at work. A large and growing number of causative agents have been identified. These occupational ‘asthmogens’ may be macromolecules of biological origin, metallic agents or synthetic chemicals. Inhaled irritants can also cause asthma without specific sensitization, either after a single acute inhalation accident (RADS) or through repeated or chronic exposure to excessive levels, for example during cleaning work. In the latter case, the presentation of occupational asthma may resemble that of allergen-induced occupational asthma because the worker may have been able to work for some time without experiencing respiratory symptoms (i.e. there has been a symptom-free latency period).
The annual incidence of occupational asthma has been estimated to be 2–5 cases per 100 000 working individuals. Thus, occupational factors play an important role not only in causing specific occupational asthma but also in favouring the development of asthma in adults. The lowest rate was recorded in the Netherlands (0.5/100,000). Early diagnosis, elimination of exposure to the responsible agent, and early use of inhaled steroids may play important roles in the prevention of long-term persistence of asthma. Persistent occupational asthma is often associated with substantial disability and consequent impacts on income and quality of life.