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September 2004

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What is mould?

Moulds are fungi, a group of very common organisms that also includes mushrooms and yeasts. Moulds are generally found in nature and are carried indoors from the outside. More than 270 species of mould have been identified in Canadian homes.

Moulds can grow indoors in wet or damp areas, including wallpaper, ceiling tiles, carpets (especially those with jute backing), insulation material, wood and drywall.

What are the health effects of mould?


Most common types of moulds are generally not harmful to healthy individuals. However, exposure to mould can cause reactions depending on overall health, age and the amount of time an exposed person spends in the home.

The elderly, pregnant women, infants and young children, people with allergies, chronic respiratory illness and/or chemical sensitivities and those with weakened immune systems are most likely to experience health effects from mould.

The most common health problems associated with exposure to mould are:
  • Eye, nose and throat irritation
  • Runny nose, sinus congestion, frequent cold symptoms
  • Increased asthma attacks
  • Allergic reactions
Anyone experiencing any of these symptoms should consult a physician.

How can I prevent mould from growing in my home?

Control humidity
  • Avoid excessively high and prolonged humidity/dampness in the home.
  • Limit the use of humidifiers. When using a humidifier, follow the manufacturer's maintenance instructions.
  • Limit the number of fish tanks and indoor plants as these can raise the humidity level in your home.
Proper ventilation
  • Turn on exhaust fans, particularly when bathing, showering, cooking and doing laundry.
  • Open windows when weather permits.
Control moisture
  • Repair all leaks and plumbing problems.
  • Thoroughly clean and dry water-damaged carpets and building materials. Discard material that cannot be cleaned and properly dried.
What should I do if I have mould?

Small areas

Small areas of mould can be cleaned using a household cleaner. A small area is fewer than three patches, with each patch less than three feet by three feet in size.
  • Scrub the area with detergent (preferably an unscented detergent).
  • Sponge with a clean, wet rag and dry quickly and thoroughly.
Always wear personal protective equipment, including a disposable dust mask (3M 8210 or equivalent) and household rubber gloves, when using any cleaner or chemical.

Larger areas

Areas of mould larger than three patches (each patch more than 3 feet by 3 feet in size) should be cleaned by professionals. Professional help can be found under Environmental Services in the Yellow Pages.

In all cases, the underlying cause of water accumulation or prolonged high humidity must be corrected or mould will continue to grow or reoccur. Regularly inspect your home for signs of moisture problems or water damage (musty odours, condensation, and discoloration).



For more information contact:

Toronto Public Health, Toronto Health Connection: 416-338-7600
Canada Mortgage and Housing Corporation 1-800-668-2642

Information contained in this Fact Sheet was adapted from the Canada Mortgage and Housing Corporation's Homeowners' Guide on Fighting Mold, and the Quebec Ministry of Health and Social Services' brochure on household mould.

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