Mould

On this page

• Health risks
• Signs of mould
• Getting rid of mould
• Preventing mould
• About mould
• Reports and publications

Excessive moisture is one of the most common causes of poor indoor air in homes, classrooms and public spaces, because moisture promotes the growth of mould and dust mites.

To prevent mould, fix any moisture problems right away and control humidity levels in your home. If you already have mould, it's important to clean it up right away.

Do you rent?

If you rent your home or workspace, speak to your landlord about any mould problems. Information on landlord/tenant issues, rights and responsibilities is available from your provincial/territorial government.

Health risks

People living in homes with mould and damp conditions are more likely to have:

• eye, nose and throat irritation
• coughing and mucous (phlegm) build-up
• wheezing and shortness of breath
• worsening of asthma symptoms
• other allergic reactions

Some people are more susceptible to the health effects of mould than others. This may include children, seniors and people with medical conditions (like asthma and severe allergies). Since some people are more sensitive than others, there is no "safe" limit for mould.

Some airborne moulds can cause severe lung infections in people with very weakened immune systems (like those with leukemia or AIDS, or transplant recipients).

If you think that your health problems might be related to mould, talk to your health care professional as soon as possible. Remove any mould that already exists, and take steps to prevent it from growing.

Signs of mould

In most cases, there is no need to measure the actual concentration of mould in your indoor air, or to determine the specific species of mould. You just need to find and fix the moisture and mould problems.

Not all mould is obvious to find. It is important to check for mould anywhere that is damp, especially where water damage has happened.

Inspect your home for visible signs of mould or areas with too much moisture. Look for stains or discolouration on floors, walls, window panes, fabrics and carpets. See if you smell a musty "earthy" odour. If needed, contact an expert for help.

Getting rid of mould

You can generally clean small and medium sized areas of mould by yourself. You should consider getting professional help with extensive mould growth.

Health Canada classifies the amount of mould as:

• Small, if there are 1 - 3 patches, each less than 1 m² (10 square feet) in size
• Medium-sized, if there more than 3 patches or if the patches are greater than 1 m² but less than 3 m² (32 square feet)
• Extensive, if the patch is larger than 3 m²

If the contaminated surface is small to moderate:

• Wear safety glasses or goggles, a disposable N95 respirator (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.
• Susceptible people should not be in the same room or near the area where the mould is being cleaned up.

If the affected area is large:

• Take precautions to protect your health.
• Consider hiring a professional to clean it up, especially if there is a large amount of mould or if the mould keeps coming back after you clean it.
• A large amount of mould is often the result of a larger problem (like a leak in the foundation or a major flood), which you may need a professional help to fix.

Once clean-up is done, be sure to fix the underlying cause (water damage, too much humidity or not enough ventilation) to prevent more mould from growing again.

Preventing mould

A major cause of poor indoor air quality is poor ventilation (that is, not enough exchange of air between the outside and inside). Common problem areas include kitchens, bathrooms and basements.

Prevent mould from growing by making sure you:

• look for damp spots in your house
  • check basements, closets, window sills, roofs, and around sinks, tubs and pipes
• fix damp spots right away
  • repair any water leaks as soon as you notice them
  • clean up immediately after any flood
• use fans
  • use kitchen and bathroom exhaust fans when cooking or showering
  • let the fan run for a few minutes after you are done
• vent outside
  • make sure your clothes dryer, stove, kitchen and bathroom fans all vent to the outdoors
• seal tubs and sinks
  • make sure the seal is tight so water doesn't leak into the walls
• throw out basement clutter
  • cardboard boxes and old clothes are great places for mould to grow
• keep your home well ventilated
  • open windows in dry weather or use fans as needed
• reduce humidity
  • maintain relative humidity levels between 30% and 50%
  • if needed, use a dehumidifier or air conditioner to reduce humidity levels
  • you can use a hygrometer (an inexpensive tool available at most hardware stores) to measure humidity
• clean
  • regularly clean and disinfect anything that holds water, like humidifiers, de-humidifiers and air conditioners

About mould

Mould is the common word for any fungus that grows on food or damp building materials. It often looks like a stain and comes in a variety of colours. In some cases, however, mould may not be visible but may have a musty odour. If it is allowed to grow, mould can contribute to poor indoor air quality.

Mould can grow in damp or wet areas in your home caused by water leaks, flooding, or high humidity that can result from everyday activities like cooking or showering. It can grow on wood, paper, fabrics, drywall and insulation. It can hide inside walls or above ceiling tiles. When mould finds a damp place to grow, it can contribute to poor indoor air quality and health problems.

Reports and publications

• Guide to Addressing Moisture and Mould Indoors
• Residential Indoor Air Quality Guideline: Moulds
• Virtual house tour
• Infographic: Mould