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Environmental Health

Mouldy Homes and Buildings: Topic Overview

​​​​​What are moulds?

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 that have been damaged by water. Mould reproduces by releasing millions of very small spores and by spreading mycelial fragments. Mycelial fragments are the thread-like fibres that form the body of the mould.

Mould spores and fragments are carried through the air and settle on different surfaces. They need a food source and moisture to grow. Toxins can be found on the mould spore and mould fragments. This means that they can also be found on the material the mould grows on. Growing mycelia can release a smell into the air (smells musty).The mould spores and mycelial fragments may settle on indoor surfaces as a part of household dust.

In nature, moulds cause dead plant material to rot. In spring and fall, airborne mould levels increase because of mould breaking down organic materials (like grass and leaf litter).

What are the concerns about indoor mould?

The places where mould grows indoors are usually places that have a water leak, are very humid, or have condensation problems. Health problems seen with high levels of airborne mould spores include allergic reactions, asthma episodes, irritations of the eye, nose and throat, sinus congestion, and other respiratory problems.

Can being exposed to mould affect my health?

We are all exposed to mould, both indoors and outdoors, every day. It usually doesn’t make us sick. The indoor levels in buildings without water damage are normally lower than outdoor levels. In spring and fall, or during long periods of wet weather, the airborne mould level in the outdoor air normally goes up. This can make allergies and asthma worse.

Health risks go up when people are exposed to higher mould levels when indoors, where people spend more time (like at home, school, or work). The health effects depend on the type and amount of mould, and a person’s health.

Being exposed to mould can cause irritant or allergic responses. These can include:

  • wheezing or trouble breathing
  • nose, eye, or throat irritation
  • nasal or sinus congestion
  • a dry, hacking cough
  • skin irritation or rashes

For infants, the elderly, or those who already have a respiratory illness or mould allergies, being exposed to even a low level of mould can cause symptoms. People with weaker immune systems or who are regularly exposed to high levels of mould may (but rarely) develop a fungal infection.

Anyone who finds that they’re sick often should see a doctor.

However, showing signs and symptoms doesn’t always mean that you have mould in your house. Your symptoms could be caused by being exposed to or being sensitive to other indoor and outdoor allergens and pollutants. These include:

  • pet or animal dander
  • seasonal pollens
  • indoor dust mites
  • exposure due to the job or renovations
  • second-hand smoke
  • emissions from appliances that ignite (like the furnace or gas stove)
  • emissions from consumer goods (like cleaning products, cosmetics, air fresheners)

Current as of: November 3, 2016

Author: Environmental Public Health, Alberta Health Services