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Moulds are a type of fungus commonly found all over the world. Moulds are spread through the air by spores that are too small to be seen by the naked eye. View the fact sheet below or this web page for more information on mould.



How do I know if I have mould?

Mould can cause discolouration and odours.


Mould can be any colour: black, white, red, orange, yellow, blue, violet, etc.
Not all discolourations are caused by mould.


Musty or earthy smell may be present.

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What does mould need to grow?

Mould growth requires:

  • warm temperatures,
  • nutrients or a growth medium, and
  • water.

As most homes and buildings provide the right temperature and growth medium, a mould growth problem can most often be caused by a moisture problem or high humidity.1

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What is the Canadian guideline for mould?

No exposure limits have been set by Health Canada. Health risks depend greatly on exposure and each person’s sensitivity.1 In the absence of exposure limits, tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants.1

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Why is mould a public health concern?

Mould growth can influence the indoor air quality, as moulds can release small particles, such as spores and mycelial fragments into the air.1 These small particles are able to be inhaled by humans, and can penetrate deep into the lungs.1

Some people are more susceptible to mould than others, such as; the elderly, young infants, people who are immunocompromised, or those with an existing respiratory condition. Exposure to mould can be associated with asthma-related symptoms such as chronic wheezing, irritation symptoms, and non-specific symptoms.1

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How do I prevent mould growth in my home?

Health Canada recommends:1

  • to control humidity (i.e. prevent high humidity),
  • to diligently repair any water damage in your premises, and
  • to clean thoroughly any visible or concealed mould growing in the building.

These recommendations apply regardless of the mould species found to be growing in the building.

Read more about preventing mould on Health Canada's web page.

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How do I clean mould?

If the contaminated surface is small to moderate:2

  • Wear safety glasses or goggles, a disposable N95 mask, and household disposable gloves.
  • You may want to isolate the area by taping plastic sheeting to the walls and ceiling to prevent the spread of dust and mould particles.
  • Vacuum the area with a HEPA vacuum cleaner before and after cleaning.
  • Clean the mould by using water and dish detergent. There's no need to use bleach. When cleaning drywall, use a damp cloth so you don't make the drywall wet.
  • Sensitive people should not be in the same room during the work and may want to leave the house until the mould is removed.

You might consider hiring a professional if there is a large amount of mould (if the patch is larger than 3 m²) or if the mould keeps coming back after you clean it. A large amount of mould is often the result of a larger problem, such as a leak in the foundation or a major flood, which may require professional help to fix.2

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What should I do if I am concerned about mould in my rental unit?

  • For mould in bathrooms or window sills, simply clean the area with soap and water.
  • If the mould is caused by a water leakage either from outside or a broken pipe, or a flooding incident, etc., notify your landlord or property manager in writing, and allow a reasonable amount of time for actions to be taken.
  • In the meantime, increase ventilation by opening windows and using fans to circulate air.

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Additional Information

For more information visit the Government of Canada's Mould web page.

View Health Canada's Indoor Air Quality Checklist (PDF 307KB) for steps you can take to protect yourself and your family from indoor air pollutants, including mould.

To speak to a Public Health Inspector on the Environmental Health Team about mould, please call:

  • 519-663-5317


Please note: Where indicated, the source of the information on this web page is the Government of Canada’s Residential Indoor Air Quality Guideline: Moulds or Mould websites. The information is a copy of the version available at the URL in the references section below.

Date of creation: September 11, 2013
Last modified on: December 21, 2021


1Government of Canada. (2016, January 12). Residential indoor air quality guideline: moulds. Retrieved from