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Moulds in Indoor Air

Concern about indoor mould exposure has been increasing as the public becomes aware that mould exposure can cause various health effects and symptoms, including allergic reactions. Moulds can be found almost anywhere. They grow on virtually any organic substance, as long as moisture and oxygen are present. Some moulds can grow on wood, paper, carpet, foods and insulation.

Image by Olena Shmahalo

Mould growth occurs when excessive moisture accumulates in buildings or on building materials, particularly if the moisture problem goes untreated. Air conditioning systems provide an excellent environment for mould growth. The cooling coil, which cools the air, has moisture, a cool temperature and dust particles for food. All air passes through this coil and, in many cases, over bacteria and mould. It is impossible to eliminate all moulds and spores in an indoor environment. However, mould growth can be prevented by controlling moisture and applying biocides to air conditioning coils.


Moulds reproduce by making spores that usually cannot be seen without magnification. Mould spores waft through the indoor and outdoor air continually. When mould spores land on damp spots, they begin to eat whatever they are growing on to survive.


There are many types of moulds, and they all have the potential to cause health effects. Moulds can produce allergens that trigger allergic reactions or asthma attacks. Others are known to produce potent toxins, irritants or both. Potential health concerns are an important reason to prevent mould growth and clean up any existing mould growth.

Things You Should Know About Mould

  • Potential health effects and symptoms associated with mould exposure include allergic reactions, asthma and other respiratory complaints.

  • There is no practical way to eliminate all mould and mould spores in an indoor environment. We can, however, control mould growth and prevent problems.

  • Prevent condensation. Reduce the potential for condensation on cold surfaces by adding insulation.

  • Moulds can be found almost anywhere; they can grow on virtually any substance if moisture is present. Some moulds can grow on wood, paper, carpet and food.

  • In areas where moisture is always present (like air conditioning coils), biocides will control bacteria and mould.

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