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What is Occupational Asthma?

Occupational Asthma (OA)

Occupational asthma occurs when a person, who (usually) did not previously have asthma, is exposed to something in the work environment and then develops asthma caused by the work exposure(s).  It can have serious effects on the severity of asthma and may require a job change .For people who already have asthma, it is less common to develop occupational asthma on the job. But when this does happen, it can have serious effects on the severity of asthma and may also require a job change.


  • People who have occupational asthma and move to a different workplace can also develop work-exacerbated asthma.

When would you notice your symptoms?

If something at work has caused your asthma symptoms, they may get worse every time you are exposed to it. The symptoms do not start for the first time on your first day of exposure but may develop weeks, months or even years after starting your job.

Once occupational asthma starts, your symptoms may get worse with every exposure and your asthma may get progressively worse. Your asthma could be triggered:


  • Within minutes of an exposure, or
  • Only after several hours of exposure (e.g.,during the day), or
  • After leaving the work shift (e.g. symptoms at night if you worked the day shift)


Because your symptoms may not appear immediately, it may be difficult to recognize the connection to your work. There will usually be an improvement in asthma symptoms on your days off work, especially after 2 or 3 days off, or when you're on a holiday.

Occupational sensitizers

Occupational sensitizers are substances in your work place that can cause occupational asthma to develop. They are often materials that can cause allergic reactions as well (e.g. runny and itchy eyes and nose, sneezing). If you already have allergies, you may be more likely to become sensitive to one of these occupational sensitizers. There are two types of occupational sensitizers:

  1. High-molecular weight agents - examples include:
    • Enzymes (e.g., in detergents or laboratories) and moulds
    • Proteins from animals, plants, foods, insects and fish
    • Fish and shellfish such as snow crab in fisheries and fish processing industries (particularly in Atlantic Canada).
    • Wheat or other flour exposures in bakers
  2. Low-molecular weight agents - examples include:
    • Chemicals
    • Isocyanates in spray paints, some glues, foundry moulds, polyurethane foam used in foam products or insulation. Common jobs are roofers, spray painters in automobile industry, insulators, and polyurethane workers.
    • Western red cedar dust in the logging industry in British Columbia.




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