With smog, pollen and severe weather changes, you might think that you’re more likely to encounter more triggers outdoors than indoors. In fact, the opposite is true. Canadians spend 90% of their time indoors. This, along with changes in how our homes are built, is has lead to poor indoor air quality and more triggers, in our homes.

Fortunately, a great deal has been learned about asthma triggers that exist inside. By educating yourself about indoor hazards, you’ll discover simple ways to reduce their levels.

Dust Mites

Dust mite allergy is a common problem for people with asthma. The excretions and body parts of these tiny, spider-like creatures can be a powerful trigger of asthma symptoms.

Dust mites congregate in soft-surfaced places where there is an abundant food supply. Dust mites feed off shed human skin and are thus found in bedding, mattresses, pillows, sofas and carpets.

Effective strategies for minimizing dust mites are:

  • Use a dehumidifier in damp area. Keep the humidity level below 50 %. Dust mites can’t survive in dry environments.
  • Remove carpets, especially in the bedroom.
  • Launder bed linens in very hot water (55 degrees Celsius).
  • Encase your pillow, mattress and box spring in mite-allergen impermeable encasings.


Cockroaches are one of most hated household pests, and for good reason. Not only are they a terrible nuisance, their feces have been shown to trigger symptoms in individuals with asthma.

If your home has cockroaches, make sure that food and water are never left where they can get at them. To ensure they leave and never come back, call a professional exterminator.

Indoor Moulds

Moulds are fungus that can be found just about anywhere it’s damp and where air flow is minimal, like basements and bathrooms. Their airborne spores can trigger asthma symptoms, but there are many ways to avoid them. The best way is to keep your home dry and clean.

  • Monitor the humidity level in your home with a hygrometer and keep the level between 40-45%.
  • Make sure your home is well ventilated.
  • Remove carpeting where possible. If carpet is kept, vacuum thoroughly and frequently using a vacuum cleaner with a HEPA filter.
  • Clean moldy areas, especially in bathrooms, with an anti-mould cleaner like vinegar or a chlorine-bleach solution. When using these chemical, be sure to use them in a well ventilated area.
  • Ensure that you have proper drainage around your house.
  • Use a dehumidifier if humidity is higher than 50% (basements).
  • Always use bathrooms and the kitchen fans.
  • Reduce the number of your house plants.
  • Do not have carpet in bathrooms or directly on concrete floors in the basement.

Viral Infections

Viruses can both cause asthma episodes and make people with asthma more sensitive to other asthma triggers.

Viral triggers include:

  • The rhinovirus (common cold)
  • Respiratory syncytial virus (RSV)
  • Certain flu viruses

Your healthcare team can tell you about ways to avoid viral infections, and what to do when you get sick.

People with asthma are encouraged to get the flu shot in the Fall.

Chemicals and Fragrances

Asthma attacks can be triggered by exposure to chemical fumes (such as laundry detergents, cleaning products, hairspray, scented cosmetics, perfume, paints, etc). Many people with asthma are affected by airborne chemicals and fragrances. They may be exposed to them in the home, or even at work.

At home, chemicals and fragrances are reasonably easy to control. If you have paints or other volatile products in your house, you can get rid of them or seal them carefully and place them in a garage or shed. If you’re sensitive to heavy perfumes, try not to use products that use them.

Laundry detergent is an often unrecognized source of asthma triggers. Most laundry detergents contain high concentrations of irritating fragrances. Try to use only all-natural, unscented and avoid the use of dryer sheets which can be heavily doused in synthetic fragrance.

Occupational Asthma

If you have any of the following jobs, you may be at risk for occupational asthma:

Grains, flours, plants and gums

  • Bakers, chemists and farmers

Animals, insects and fungi

  • Poultry workers, entomologists, laboratory workers and veterinary professionals


  • Aircraft fitters, brewery workers, pulp mill workers, electronic workers, hairdressers, refrigeration workers, resin manufacturers and dye weighers

Isocynates and metals

  • Car sprayers, boat builders, foam, TDI and refrigerator manufacturers, platinum chemists and refiners, printers and laminators and welders

Drugs and enzymes

  • Ampicillin, detergent and enzyme manufacturers, pharmacists and pharmaceutical workers


  • Carpenters, millers, saw-mill workers, wood finishers and machinists

To determine whether you’ve developed occupational asthma, ask yourself the following questions:

  • Did your asthma symptoms appear within weeks or months of starting a new job, or moving to a new area within your current job?
  • Do your asthma symptoms regularly and predictably occur while you’re at work or within a few hours of leaving the workplace?
  • Do you notice that your symptoms improve on weekends or when you’re on vacation, and then get worse when you go back to work?
  • Do other people at work have the same symptoms?

If you suspect you have occupational asthma, talk to your doctor, who may refer you to a respirologist for further assessment.

If your employer has taken every preventive measure possible and your symptoms are still severe, you may have to consider switching careers. Remember, you can always talk to your doctor or asthma educator if you think your job is making you sick.

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Do You Know Your Triggers?

Learn what things can cause asthma symptoms
– and how you can avoid them. Plus, find out
why, despite what you might think, you could be
more affected by indoor triggers than outdoor triggers.
For more information, read the Breathe Easy Booklet #2: