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Triggers are the things that can cause your asthma symptoms. Each person has their own set of asthma triggers. Over time you can figure out what your asthma triggers are and take steps to reduce your exposure.

There are two types of asthma triggers:

  1. Allergens
  2. Irritants

Allergens only affect you if you are allergic to them. Irritants can bother anyone with asthma.


When you breathe in one of your allergens, your immune (defence) system is ready to react to it in order to remove it. It is this allergic reaction that causes inflammation, swelling, extra mucus, and a tightening of your airways (bronchoconstriction). This blocks the flow of air into and out of your lungs and causes your symptoms.

The most common allergens include:



Although food is not a common trigger of asthma, additives such as sulphites may trigger asthma symptoms in some people.


There are many possible irritants where people live, work, or go to school that can trigger asthma symptoms. You may notice that you get asthma symptoms from some of the following irritants.

Indoor Irritants

Most people are aware of the risks from outdoor air pollution. However, indoor air pollution is often worse than outdoor air. We also generally spend a lot more time indoors than outdoors.

The following are common indoor irritants that can trigger asthma symptoms.

A cold or the flu often leads to asthma symptoms.

Outdoor irritants

There are many outdoor irritants that can cause asthma symptoms. They include:

  • Air pollution from vehicles, factories, power plants, etc.
  • Cold air
  • Hot, humid weather
  • Smoke from wood burning, backyard burning, and forest fires

Air Quality Health Index (AQHI)

Current air pollution levels and forecast maximums can be found at www.airqualityontario.com. The Air Quality Health Index (AQHI) reports on the health risks associated with air pollution at a given time.

The AQHI measures these three air pollutants that are known to be harmful:

  1. Ozone (O3)
  2. Particulate matter 2.5 microns (PM2.5) in diameter and less (1 micron is 1/1000 of a mm)
  3. Nitrogen dioxide (NO2)

The AQHI provides the combined overall general health risk from these three pollutants. Follow the AQHI reports and forecasts, and take steps to reduce your exposure. Adjust your outdoor activity accordingly.

Follow the recommended steps to take based on the AQHI levels and whether or not you are in an “at risk” group (e.g., asthma).

Sign up for air quality alert notifications through Air Quality Ontario.


Medication triggers

Certain medications can trigger asthma symptoms in some people. Let your health-care providers know about all of the medications you take – including non-prescription and herbal treatments. Check with your health-care provider before you take any new medication.

The following medications may cause asthma symptoms in some people:

  • Non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, naproxen—these are often used for cold/flu symptom relief and to relieve pain (e.g., for arthritis, headache, and muscle pain). If one NSAID triggers your asthma symptoms, other NSAIDs will also likely trigger your asthma symptoms
  • Beta blockers used to treat high blood pressure, angina, glaucoma, and sometimes tremor
  • ACE inhibitors (for high blood pressure and heart disease) can cause a dry cough

If you know that you react to a certain medication, here are some ways to protect yourself:

  • If you take a medication and develop asthma symptoms, stop taking that medication and tell your health-care provider and pharmacist right away—ask them for advice on which medications to avoid
  • Work with your health-care provider to find an alternate medication that you do not react to
  • If you need to avoid certain medications, always check medication labels


Managing your asthma


Regular exercise is a very important part of a healthy lifestyle. If you manage your asthma well, you should be able to exercise. Most people who manage their asthma well should not need to take a reliever inhaler (usually a blue inhaler) before exercising. If you need to take your reliever inhaler more than three times a week (including before exercise) see your health-care provider to find out how to get your asthma under control.

Benefits of regular exercise include:

  • Helps you to maintain a normal weight
  • Reduces your risk of:
    • Osteoporosis
    • Heart disease
    • Diabetes
    • Some cancers
  • Improved mental health
  • Better able to do your normal daily activities
  • Prevent falls as you get older
  • Longer life

Here are some tips that can help you stay active:

  • Do not start exercising if you have any asthma symptoms
  • Warm up by starting at a slower pace—increase the pace slowly
  • If you need to take a reliever inhaler before exercising, it should be taken about 10-15 minutes before the activity
  • If you develop asthma symptoms while exercising, stop immediately—use your reliever inhaler and do not start again unless your symptoms are completely gone.
  • Consider exercising indoors when outdoor conditions may trigger your asthma (e.g., when there is high air pollution or pollen levels, cold air, or hot humid air)
  • When exercising in cold weather, cover your nose and mouth with a scarf or cold weather mask
  • If symptoms continue, your asthma may not be under control—work with your health-care provider to improve your asthma management


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