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Environmental and Workplace Health

Effects of Mould on Health

There is increasing concern about the health effects of indoor mould growth because of a probable link to a wide range of symptoms and illnesses.

North American and European studies show a relationship between mould and damp conditions, and an increase in the following symptoms:

  • Eye, nose and throat irritation;
  • Coughing and phlegm build-up;
  • Wheezing and shortness of breath; and
  • Allergic reactions.

Although it seems clear that exposure to mould can worsen the symptoms of asthma, it is still unclear whether or not it actually causes asthma in otherwise healthy people.

To avoid potential health problems, Health Canada recommends that you remove any mould that already exists, and take steps to minimize dampness in order to reduce the likelihood of future mould growth. Since some people are more sensitive than others, it is not possible to establish a "safe" limit for mould.

If you suspect that you or someone else's health problems might be related to exposure to mould, talk to your doctor as soon as possible. Also, make sure you take steps to remove mould safely and deal with the conditions that allowed it to grow in the first place.

If you want to know more, see Health Canada's Residential Indoor Air Quality Guideline for Mould which summarizes the latest Canadian and international research on the health effects of mould.

People at Special Risk

Some people are more vulnerable to the effects of mould than others, for example, people with weakened immune systems. Evidence shows that some airborne moulds can cause severe infections in people with leukemia or AIDS, as well as transplant recipients and those with other conditions that weaken the immune system.

Are some moulds toxic?

You may hear mention of so-called "toxic" mould species, often referring to "black mould" or the genus Stachybotrys. While it is true that some moulds do naturally produce toxic substances (known as mycotoxins), there is not sufficient evidence that these moulds have different or greater health effects than other moulds. All moulds pose a risk to respiratory health and should be removed, regardless of the type of mould.