Date: July 17, 2019

Showers or thunderstorms ending near noon then mainly cloudy with 40 percent chance of showers. Risk of a thunderstorm late this afternoon. Local amount 15 to 25 mm. High 28. Humidex 37. UV index 7 or high.


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This page was reviewed or revised on Friday, December 11, 2015 1:55 PM

Mould is a fungi. It can grow on building materials, in the home or in other buildings.1

What does mould need to grow?

  • warm temperatures
  • nutrients or a growth medium
  • 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

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.

What are the health effects of mould?

Exposure to mould is associated with an increased number of asthma-related symptoms such as chronic wheezing, irritation symptoms, and non-specific symptoms.1

What is the Canadian guideline for mould?

No exposure limits have been set by Health Canada. Health risks depend greatly on exposure, each person’s allergic sensitivity, and the large number of mould strains, which can each cause different symptoms in different people.1

Health Canada recommends:1

  • Control humidity and diligently repair any water damage in residences to prevent mould growth.
  • Clean thoroughly any visible or concealed mould growing in residential buildings.

These recommendations apply regardless of the mould species found to be 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.1

How do I clean mould?

If you discover mould, follow these two steps:2

  • Clean the mouldy surface with water and dish detergent. There is no need to use bleach.
  • 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 you wear proper protective equipment, including rubber gloves, eye protection and a dust mask.2

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 also 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?

  • 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, notify your landlord or property manager in writing, and allow a reasonable amount of time for actions to be taken.
  • If no actions are taken, or your property manager refuses to address the issue, you may contact Lambton Public Health at 519-383-8331, and discuss it with a public health inspector.
  • In the meantime, increase ventilation by opening windows and using fans to circulate air.

In which situations will Lambton Public Health do an inspection?

Public Health Inspectors will carry out an inspection if all of the following conditions are met:

  • Mould is visible.
  • The property manager has been notified of the concern in writing.
  • The concern has not been addressed in a reasonable amount of time.

Additional information:

Mould: Get Rid of It! - Health Canada
Moisture Condensation Causes - Canadian Mortgage and Housing Corporation 
Indoor Air Quality Checklist (PDF) - Health Canada
Steps you can take to protect yourself and your family from indoor air pollutants, including mould.

To speak to a Public Health Inspector about mould, please call 519-383-8331 or toll Free 1-800-667-1839.


1 Residential Indoor Air Quality Guidelines: Moulds - Health Canada (2007, December 5)
2 Mould: Get Rid of It! - Health Canada (2012, March 29)

Adapted with permission from Middlesex London Health Unit