Whenever mould testing is performed people want to know whether the levels of mould detected are harmful or not. While there is enough evidence to suggest exposure to indoor mould result in an increased prevalence of asthma-related symptoms such as chronic wheezing, irritation symptoms, and non-specific symptoms it has proved difficult to set exposure limits for mould. Health Canada has issued a residential indoor air quality guideline for moulds as quoted below:

"Health Canada considers that mould growth in residential buildings may pose a health hazard. Health risks depend on exposure and, for asthma symptoms, on allergic sensitization. However, the large number of mould species and strains growing in buildings and the large inter-individual variability in human response to mould exposure preclude the derivation of exposure limits. Therefore, Health Canada recommends:

• to control humidity and diligently repair any water damage in residences to prevent mould growth; and
• to clean thoroughly any visible or concealed mould growing in residential buildings.

These recommendations apply regardless of the mould species found to be growing in the building. "

Any visible mould should be removed safely. There are mould guidelines that outline safe procedures for mould removal. Most of these guidelines are available on the internet.

If you are a homeowner or an occupant of a house and you see visible mould growth, you may want to send samples to a laboratory for testing. The lab report would tell you the types of mould species growing in the house and whether they are known to be of health concern. But remember, regardless of the types of moulds present, the mould has to be cleaned.