Topic Overview

Mould can get into a building through open doorways, windows, vents, and heating and air conditioning systems. Mould in the air outside can also attach itself to clothing, shoes, bags, and pets and can be carried indoors. Mould will grow in places with a lot of moisture, such as around leaky roofs, windows, or pipes, or flooded areas. Mould grows well on paper products, cardboard, ceiling tiles, and wood products. Mould can also grow in dust, paints, wallpaper, insulation, drywall, carpet, and fabrics.

Indoor mould (fungus) is very common in humid areas and in homes that have damp areas such as basements. Mould may trigger asthma symptoms, such as wheezing or coughing, or another allergic reaction, such as the rash of atopic dermatitis or stuffy nose of allergic rhinitis. Substances that trigger these reactions are called allergens.

Although there is no strong evidence that reducing damp areas in homes or limiting exposure to them helps decrease allergy and asthma symptoms, taking the following steps may help keep mould out of the house or limit its growth.

  • Clean washroom surfaces with soap and water, mould-killing products, or liquid bleach mixed with water. If you have mould in your home, remove it with one of these methods. Use bleach with caution, because it may irritate your nose.
  • Keep the house aired out and dry. This may be difficult in some seasons and some climates.
    • Use an exhaust fan in washrooms and the kitchen to vent excess moisture.
    • Make sure your clothes dryer vents moist air to the outside.
  • Use a dehumidifier or air conditioner during humid weather. Try to keep the humidity in the home below 50%. Moulds thrive in higher humidity. You can use a moisture or humidity meter to check how humid it is in your home. You can buy the device at a hardware store.
  • Seal off or avoid damp areas, such as crawl spaces, attics, or basements. Use a dehumidifier to control mould growth in these areas. Try to avoid materials that have been stored in these areas.
  • Remove carpeting from rooms that may have a lot of moisture, such as the washroom and basement.
  • Repair any water-damaged areas from leaking roofs or basements. Also, check the areas under sinks and around other plumbing for leaks. These areas can be prime mould-growing areas.
  • Inspect closets for items, such as shoes, that may retain moisture.
  • Add a mould inhibitor product to paint that you use in the home.
  • Store fireplace wood outside the home.

Adults spend one-third of their time and children spend half of their time in their bedrooms, so it is important that you take steps to prevent allergens in this room.

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Other Works Consulted

  • Centers for Disease Control and Prevention (2009, updated 2012). Facts about mold and dampness. Available online:


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Rohit K Katial, MD - Allergy and Immunology

Current as ofFebruary 20, 2015