Health concerns come into focus when unusual types and numbers of moulds grow indoors.
This happens when sources of moisture and areas where mould can grow combine to promote mould growth. This can lead to higher concentrations of mould indoors than outdoors and growth of toxic types of mould. The mould growth may be hidden from view, within walls, ceilings and in ventilation equipment, and still affect air quality. In 1997, the provincial Ministry of Health convened an expert panel to study the health effects of mould in indoor environments, including school accommodation. A second expert panel, convened by the province in 1999, released findings that generally concurred with those of the first panel, namely that there is a strong association between respiratory symptoms and the presence of water damage, moisture and moulds in indoor environments.