A number of industries and sources have been implicated, including[REF] high levels of dust in coal mining, gold mining, and the cotton textile industry, occupations involving cadmium and isocyanates, and fumes from welding [REF].
An acute exacerbation (a sudden worsening of symptoms)[REF] is commonly triggered by infection or environmental pollutants, or sometimes by other factors such as improper use of medications [REF].