Mould (also spelt as mold) produces tiny reproductive structures called spores. Spores are released in enormous numbers and disseminated in
air so that they are found almost everywhere. Some mould species also produce by-products called mycotoxins which can also become airborne. Several mycotoxins are highly toxic or carcinogenic. One out of every five people is likely to react to normal spore concentration by developing "hay fever" or asthma. Prolonged or repeated exposure to high concentrations of mould spores can result to sensitization even to healthy individuals. Mould related illnesses include: * lower respiratory symptoms such as coughing and wheezing, * respiratory infections such as aspergillosis, * allergic reactions, including allergic asthma and bronchitis, * unspecific symptoms, such as eye and skin irritation, fatigue, headache, nausea, and vomiting.
Which Are The Common Moulds And Why Do They Grow Indoors?
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 kitchen, bathrooms, ceilings and in 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 types that colonize 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.
