Hyperpigmented areas may persist after the lesion has resolved. Up to 15 percent of cases of asthma in adults in industrialized countries are related to occupation. Airborne dust, gases, vapors or fumes generated in the workplace cause narrowing of the airways. This narrowing is initially reversible, but persistent exposure to the allergen may result in permanent symptoms of asthma. Patients may have an initial latent period of up to several years during which they are asymptomatic despite exposure.
Early symptoms are often nasal congestion, sneezing, watering of the eyes, itching and burning.
Many agents can cause occupational asthma. Occupational asthma should be suspected when symptoms resolve during holiday periods. A person viewing it online may make one printout of the material and may use that printout only for his or her personal, non-commercial reference.