Guidelines for the clinical evaluation of occupational asthma due to small molecular weight chemicals: Report of the Subcommittee on the Clinical Evaluation of Occupational Asthma due to Small Molecular Weight Chemicals

Occupational asthma is reversible airways obstruction induced by inhaled dusts, vapors, fumes, and gases encountered in the workplace, and should be distinguished from preexisting asthma that is exacerbated by exposure to industrial irritants. There is usually a latent or “sensitizing” period-sometimes years-before the disease develops. Bronchoprovocation studies have demonstrated that occupational asthma may manifest as an immediate (usually occurring within minutes of exposure), late (beginning hours after exposure) or dual response.’ Late responses may demonstrate a circadian rhythm, lasting for weeks after initial exposure.* Overall prevalence of occupational asthma is difficult to determine. A confounding factor in the attempt to determine prevalence is that, in many instances, there may be “self-selection” by workers who leave the industry once they become affected.3 Surveys suggest that 2% to 6% of the general adult population have asthma: it is estimated that 2% to 15% of this asthma may be of occupational origin.4 This figure varies widely depending on the country, the particular industry, and the type of agent to which workers are exposed.