Mould 1001

What is Mould?

Mould is a non-photosynthetic group of eukaryotic microbes which form a large and diverse number of fungal species. Mould simply requires water and nutrients to grow. For energy, complex nutrients (biopolymers such as cellulose and starch) are broken down by enzymes into simpler nutrients which can be more easily absorbed. Hence, mould is an integral part of the cycling of organic matter in the natural environment. For this reason, mould spores are almost everywhere in the natural and built environments, which is not necessarily a reflection of building health, but testament to the evolution of fungi. The spores can remain dormant for a long duration of time and a number of mould species are extremely hardy, surviving extreme temperatures.

Can Mould Actually Harm Me?

While mould itself is not toxic, it constantly releases spores which, when ingested, can cause a variety of illnesses including decreased immune system, respiratory infections and allergies. The extent and severity of these is greatly dependant on human factors such as age, state of health and underlying diseases weakening the immune system.

Mould and fungi species produce a range of mycotoxins. Not all are toxic. These are chemical secretions from the mould/fungi and not part of the organism itself. Mycotoxins can cause a range of illnesses and in extreme cases result in neurological damage or death (mushroom poisoning is largely due to mycotoxins).

In extreme cases, especially in people with decreased immune systems (the elderly, young children, or people with underlying diseases causing immune suppression e.g. HIV) mould/fungi can enter the body and grow internally causing infection. Generally speaking, and for our purposes in assessing building health, the incidences of mould related infection are limited and are outside the capabilities of scientists. To diagnose a mould related infection a medical assessment would be required.

Mould related factors related to health include concentration, length of time of exposure, virility and viability of the organism, and whether the effect is infectious, allergenic, toxigenic or a combination of these.

Keeping Mould at Bay

Mould thrives on warm, moist conditions and will not grow without an accumulation of an excessive amount of moisture for a sufficient amount of time within an adequate temperature range and in a material or surface coating that is microbially digestible (ASHRAE 2012:8). Thus, if you can minimise the extent of the moisture, theoretically mould will not be able to grow and survive. However, this is often easier said than done. Some simple ways of doing this include (Elliott 2013):

  • Keeping your indoor relative humidity between 30-50%. This can be controlled via an air-conditioner or a dehumidifier
  • Using ventilation fans in the bathroom and kitchen to help eliminate steam from cooking and bathing from settling on any surfaces
  • Insulating your home to help control condensation
  • Repairing leaks immediately
  • Drying wet spots within 24 hours
  • Landscaping your garden in such a way that engineers water away from the house
  • Keeping gutters and drainpipes free from debris
  • Encouraging good circulation by regularly opening windows within the house, especially to areas that are little used
  • Cleaning the drip pans in the air conditioner frequently

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However, despite all your best intents and efforts in trying to keep mould away, it can still appear. As soon as you notice the presence of mould in your home or workplace (you often may smell it before you see it), you should try and eliminate it. Based upon the size and extent of the mould, it can be helpful to undertake sampling to determine the nature and potential associated harm of any mould present. Normally, both microbial swabs and microbial air samples will be taken to complete this process. Based on the results of this investigation, a microbiological report is prepared detailing the results, outcomes and provides recommendation for remediation or management.


ASHRAE, 2012, “ASHRAE Position Document on Limiting Indoor Mould and Dampness in Buildings,” ASHRAE, Atlanta

Elliott, S 2013, “How to Test for Toxic Mould,” How Stuff Works, accessed from on 26 November 2013



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