Cat. No.: H128-1/07-508E
HC Pub.: 4075E
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The word "mould" is a common term referring to fungi that can grow on building materials in homes or other buildings. Mould growth can influence air quality because both spores and mycelial fragments are dispersed into the air and can be inhaled. Their penetration into the bronchial tree depends on their size. The smaller particles penetrate deeper into the lungs.
Three features of mould biochemistry are of special interest in terms of human health:
Mould growth in a house requires the presence of nutrients, an adequate temperature, and a sufficient amount of water. The first two requirements being usually met in indoor environments, fungal growth usually results from a moisture problem (CMHC 2003). Major causes of mould growth are:
Health Canada has carried out two reviews of the scientific literature pertaining to the health effects of indoor moulds (Health Canada 1995; 2004). The Institut national de santé publique du Québec also published a review on this subject (d'Halewyn et al. 2003). The following conclusions were drawn:
These conclusions have been supported by more recent findings. In two cohort studies (Wickman et al. 2003; Jaakkola et al. 2005), significant associations were found between home dampness and the risk of developing asthma. In experimental studies, asthma-like responses were observed in mice following exposure to a typical building-associated fungus, Penicillium chrysogenum (Chung et al. 2005), and inflammatory responses were seen in rats exposed to low doses of toxins from the same species (Rand et al. 2005).
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:
These recommendations apply regardless of the mould species found to be growing in the building.
Further, in the absence of exposure limits, results from tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants.
CMHC 2003. Clean-up Procedures for Mold in Houses. Revised ed. Ottawa: Canada Mortgage and Housing Corporation. ISBN: 0-660-19227-6.
Chung, Y. J., Coates, N. H., Viana, M. E., Copeland, L., Vesper, S. J., Selgrade, M. K., Ward, M. D. W. 2005. Dose-dependent allergic responses to an extract of Penicillium chrysogenum in BALB/c mice. Toxicology 209: 77-89.
d'Halewyn, M. A., Leclerc, J. M., King, N., Bélanger, M., Legris, M. and Frenette, Y., 2002. Les risques à la santé associés à la présence de moisissures en milieu intérieur. Québec : Institut national de santé publique du Québec. 105 p. + appendices.
Health Canada 1995. Fungal Contamination in Public Buildings: a Guide to Recognition and Management. Ottawa: Health Canada.
Health Canada 2004. Fungal Contamination in Public Buildings: Health Effects and Investigation Methods. Ottawa: Health Canada. ISBN 0-662-37432-0. 47 p.
Jaakkola, J. J. K., Hwang, B. F., Jaakkola, N. 2005. Home dampness and molds, parental atopy, and asthma in childhood: a six-year population-based cohort study. Environmental Health Perspectives. 113: 357-361.
Rand, T. G., Giles, S., Flemming, J., Miller, J. D., Puniani, E. 2005. Inflammatory and cytotoxic responses in mouse lungs exposed to purified toxins from building isolated Penicillium brevicompactum Dierckx and P. chrysogenum Thom. Toxicological Sciences 87: 213-222.
Wickman, M., Melen, E., Berglind, N., Lennart Nordvall, S., Almqvist, C., Kull, I., Svartengren, M., Pershagen, G. 2003. Strategies for preventing wheezing and asthma in small children. Allergy 58: 742-747.