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Mouldy Homes and Buildings

Mould and your health

​​​​​​​​​​​​​What is mould?

Mould, also known as fungus or mildew, is a living organism. There are many species of mould. The species commonly found outdoors are also common to buildings with water damage.

How does mould grow?

Mould grows by releasing millions of small spores and spreading mycelial fragments. Mycelial fragments are the thread-like fibres that form the body of the mould. Mould spores and fragments travel through the air and settle on surfaces. They may settle indoors as part of household dust. Mould needs a food source and moisture to grow.

Where does mould grow indoors?

Indoors, mould usually grows in places that:

  • have a water leak
  • are very humid
  • have condensation problems (when water vapour turns to liquid)

Can mould cause health problems?

Most people are exposed to mould, indoors and outdoors, every day. It usually doesn’t make you sick. There’s normally less mould inside buildings without water damage than there is outside.

The risk of health problems goes up in spring and fall or when there’s lots of wet weather because there’s more mould in the air outside. You can also find toxins in mould and on the surfaces where mould grows.

There’s also a higher risk of health problems when there’s more mould in places you spend a lot of time (like at home, school, or work). The health effects depend on the type and amount of mould and your general health.

What health problems can mould cause?

Mould can cause health problems such as:

  • asthma flare-ups
  • itchy, red, or painful (irritated) eyes, nose, and throat
  • stuffy nose and blocked sinuses
  • itchy skin or rashes
  • breathing problems (such as wheezing)

For babies, older adults, or people who already have a respiratory (breathing system) illness or mould allergies, even a small amount of mould can cause symptoms. People with weaker immune systems or who are regularly around a lot of mould may (but rarely) get a fungal infection.

If you find that you get sick a lot, see your doctor.

If I have symptoms, does it mean I have mould in my home?

Having the symptoms of a mould allergy doesn’t always mean you have mould in your home. Other things can cause your symptoms, such as:

  • pet or animal dander
  • seasonal pollens
  • indoor dust mites
  • dust or particles (from your job or renovations)
  • second-hand smoke
  • emissions (gas or particles) from appliances that light up like the furnace or gas stove
  • emissions from products like cleaning products, cosmetics, and air fresheners


Current as of: February 18, 2021

Author: Environmental Public Health, Alberta Health Services