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Mould and Your Health

What is mould?

Moulds are members of the fungus family and can be found almost anywhere, indoors and outdoors. Moulds spread by releasing tiny seed-like particles called spores into the air. Some moulds can be harmful to some individuals, if inhaled or swallowed.

Can moulds affect my health?

Not all moulds cause health effects. Moulds can pose a health concern under certain conditions. Factors that increase the risk of illness include:

  • susceptible individuals – young babies, asthmatics and persons who have poor immune systems (such as those undergoing cancer treatment and persons with HIV).

  • high levels of exposure – exposure to large numbers of spores over a long period of time.

  • species of mould – some types of moulds produce a toxin which may pose a greater risk.

Although effects of moulds on the general population are less well known, this does not mean that mould growth indoors should be ignored. Efforts should be made to keep mould growth to a minimum.

What are the health effects of mould?

Inhaling mould spores can cause allergic symptoms such as wheezing, sneezing, coughing, and nose, throat and eye irritation. Breathing large amounts of mould spores can cause a serious allergic reaction called ‘hypersensitivity pneumonitis’. In a few people, other health effects may include:

  • allergic reactions – a significant portion of asthmatics are allergic to moulds (10-30%), exposure to mould could bring on asthma attacks

  • infection mechanisms – individuals with weakened immune systems may be at risk for infection due to greater exposure to mould

  • irritative conditions – long term exposure to moulds has been suspected in a number of non-specific respiratory and flu-like symptoms, headaches, skin problems, and impaired immune functions

What should I do if I experience symptoms?

If you or your child experience symptoms that are severe or long lasting you should see your doctor. The effects of moulds are thought to be rare so if you are experiencing “flu like” symptoms it is more likely because you have a “cold” or the “flu”.  Mentioning that you have been exposed to moulds will however help your doctor with his/her diagnosis.

Where do moulds grow?

Mould can develop in warm and wet indoor areas such as showers, basements and cold wall spots where dampness occurs due to condensation. Moulds can grow on any damp or humid surface. Cellulose based products such as paper and the backing on jute carpet are also likely places for growth.

What can I do to control mould?

There are a few things you can do to prevent mould:

  • repair all water leaks

  • caulk around doors, windows, bathtubs and shower stalls

  • ventilate high moisture areas (e.g., bathroom and kitchen exhaust fans) and vent clothes dryer to the outside

  • keep humidity below 40%

  • use an air conditioner or dehumidifier during humid months

  • avoid carpeting in bathrooms and basements

  • clean bathrooms regularly with disinfectant

How do I clean-up existing mould areas?

Moulds should not be allowed to grow indoors. If they are in your home they should be cleaned up. If they are in your workplace or school, you should bring it to the attention of persons responsible for the building. The source of the water problem must first be corrected. Repair water leaks in roofs or plumbing. Consider the drainage around the exterior of the building. Surfaces with mould should be cleaned using the following (for cleaning procedures after a flood refer to our fact sheet Cleaning After a Flood):

  • washable surfaces – unscented dish washing detergent and water

  • wood surfaces – unscented detergent and water

  • rotting wood should be replaced

  • drywall – use a bit of detergent and water or baking soda water, do not allow the drywall to get too wet

As a precaution while cleaning up a small area of mould, consider using goggles, gloves and a high particular matter mask. Sponge or scrub surfaces, and then rinse with a clean wet rag or sponge, rinse washable items with running water and let dry. If the area cannot be cleaned (like wet broken ceiling tiles), is too damaged or is disposable (like cardboard boxes), discard the material and replace with new. It may be necessary to do a more extensive clean-up in the home (carpets, crawl spaces, heating ducts) if you have a wide spread mould problem. If mould growth is extensive throughout the house, professional assistance may be required.

For more information, call the Health Unit toll-free at 1-866-888-4577 and speak with a Public Health Inspector.

Additional Resources:

Mould in Your Home - video, HKPR District Health Unit

Cleaning and Removing Mould - HKPR

Mould and Your Health - Health Canada


Materials on this page adapted with permission from Simcoe Muskoka District Health Unit