Mould and dampness

Mould can cause serious symptoms and should be tackled immediately.

Moisture is one of the largest determinants of poor indoor air quality and is directly related to the growth of mould. Indoor moisture/dampness can be caused by water damage, showering, bathing, cooking, non-functioning exhaust vents, plumbing leaks, and condensation. Indoor moisture/dampness can be combated by using dehumidifiers, ensuring plumbing and exhaust vents are working properly and by installing insulated windows.


Mould is a fungi. It can grow on building materials in the home or in other buildings. As most homes and buildings provide the right temperature and growth medium, a mould problem is often caused by a moisture problem or high humidity.

Why is mould a public health concern?

Mould growth can influence the indoor air quality, as mould can release small particles into the air. These small particles can penetrate deep into the lungs. Some people, such as older people, infants, people who are immunocompromised, or those with an existing respiratory condition, may be more susceptible to the health effects of mould exposure.

What are the health effects of mould?

Exposure to mould can be associated with an increase in eye, nose and throat irritation, coughing, wheezing, shortness of breath, and allergic reactions.

How much mould needs to be present for it to be a health hazard?

No exposure limits have been set by Health Canada. Health risks depend greatly on exposure, each person’s allergic sensitivity, and the specific mould species involved. A large number of mould species exist, each of which can cause different symptoms in different people.

Health Canada recommends:

These recommendations apply regardless of the mould species found growing in the building. Further, in the absence of exposure limits, results from tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants.

How do I clean mould?

If you discover mould, follow these two steps:

  1. Clean the mouldy surface with water and dish detergent. There is no need to use bleach.
  2. Fix the underlying cause, whether it is due to water damage or too much humidity. In a rental unit, notify your landlord in writing if the mould is a recurring problem.

Note: When removing mould, it is recommended that you wear proper protective equipment including rubber gloves, eye protection, and a dust mask.

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.

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

If action is not taken, or your property manager refuses to address the issue, you can submit your question or complaint electronically or call 705.522.9200, ext. 464 (toll-free 1.866.522.9200) and discuss it with a public health inspector.

This item was last modified on August 16, 2019