Work-exacerbated asthma (WEA) is the term used to describe the worsening of asthma related to work but not the causation of asthma by work. It is common and has been reported to occur for 21.5% of working asthmatics on average. The frequency and severity may range from a single mild exacerbation that may lead to no time lost at work up to daily or severe exacerbations that may require a permanent change in work. Reports from general population surveys and primary care settings include more patients with short-term or mild exacerbations while those from tertiary care settings reflect the more severe end of the spectrum of severity or frequency, with socioeconomic outcomes that are similar to those of occupational asthma. In the minority of patients with the WEA, whose asthma starts while working, the differential diagnosis includes sensitizer-induced or possible irritant-induced occupational asthma. Optimizing work exposures and asthma management may improve outcome and prevent exacerbations. Worker education and screening of working asthmatics by primary health care workers may also prevent morbidity.