More than 150 mould species have been reported from indoor environment. Fortunately, not all these are harmful to most people. Moulds will grow virtually everywhere indoors as long as nutrients and conditions for growth are favourable. We commonly see moulds in the kitchen, bathrooms, ceilings and in the basements of houses and other buildings.



Moulds require moisture, nutrients and suitable temperature for them to grow. The level of moisture (usually referred to as water activity) in building material determines not only whether mould will grow or not but also the types that colonize the material. Damp materials with a water activity value equal to or greater than 0.90 (equivalent to 90% relative humidity) are usually colonized by strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp. Growth of these moulds is an indication of very damp to wet conditions. Materials with a water activity value ranging from 0.90 - 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.

Is Sampling And Testing For Indoor Mould Necessary?

Yes. The building occupants need assurances that they are not being exposed to moulds that may cause health problems. Testing is important so as to:

How Can We Control Mould Growth?

Mould growth can be controlled by maintaining indoor relative humidity within the range of 30-60 % and ensuring that any water leakage or flood is attended to immediately. Use of biocides to control mould in indoor environment is generally not recommended due to associated health risks and the fact that these chemicals may not be effective against all moulds and are effective for only a limited period of time.