What You Should Know About Mould Allergies And Other Related Illnesses


Mould (also spelt as mold) produces tiny reproductive structures called spores. Spores are released in enormous numbers and disseminated in the 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 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:

  • to determine the presence or absence of airborne spores, their composition and concentration in situations where occupants experience mould related ill health but with no obvious mould growth,
  • to determine if spores from visible mould growth sources had become airborne,
  • to detect and quantify certain mould species,
  • to determine the efficacy of mould remediation.

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.

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Author: Piyawut Sutthiruk

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