This resource is provided to help Australian businesses and organisations understand the issues surrounding mould.



What is mould?

Moulds are simple, microscopic organisms that are present throughout our environment, both indoors and outdoors. Moulds, along with mushrooms and yeasts are fungi and play a vital role in the Earth's ecology by decomposing organic material.

For moulds to develop they do not need sunlight and require only an organic substrate, moisture and the right temperatures to proliferate. Unlike plants, mould cannot manufacture their own nutrients and grow by digesting the organic material on which they are imbedded and absorbing the released nutrients. Because of this digestion, moulds gradually destroy whatever they grow on and can be seen in the form of discolouration, frequently green, grey, brown or black but also sometimes white and other colours.

How are you exposed to moulds?

Exposure to mould is unavoidable except when the most stringent of air filtration, isolation and environmental sanitation measures are observed such as hospital isolation units. It is common to find mould spores in the air inside homes, with most of these spores entering from outdoor sources by circulating through doorways, windows, heating, ventilation systems, and air conditioning systems and also by the deposition of spores on people and animals, providing carriers of mould into these indoor environments.

In the indoor environment mould proliferates in areas characterised by excessive moisture. Mould growth is especially common on materials or structures that remain wet for 48-72 hours and hence is a common problem after water intrusion from flooding. The four most common indoor moulds are Cladosporium, Penicillium, Aspergillus and Alnternaria.

Individuals can be exposed to mould through skin contact, ingestion of contaminated foods, hand to mouth contact after handling mouldy materials, or more commonly through the inhalation of mould spores or mould-related products.

What are the health effects of mould exposure?

Mould can affect human health in a number of ways. Possible responses however generally fall into one of the three groups: allergic reactions; infections; or toxic responses. Responses range from minor, serious or negative and can be temporary, long-term or permanent and may vary over time. Those most of risk include the age susceptible and those with pre-existing medical conditions or allergy problems. Typical symptoms that mould-exposed persons report (alone or in a combination) include:

  • Eye irritation (burning, watery or reddened eyes)
  • Respiratory problems (such as wheezing, coughing, or difficulty breathing)
  • Skin rashes or irritation
  • Headaches and fatigue
  • Nose or throat irritation
  • Nasal and sinus congestion

Allergic Reactions:

Approximately 5% of the population is predicted to have, at some time, allergic symptoms from moulds. The most common symptom associated with mould exposure is hypersensitivity. Immediate hypersensitivity is immunoglobin E (IgE) mediated allergy to fungal proteins. This reactivity can lead to allergic rhinitis or allergic asthma that is triggered by breathing in mould spores or hyphal fragments. Immediate hypersensitivity is most common in atopic individuals i.e. those who already have allergic asthma or allergic rhinitis or atopic dermatitis and manifest allergic antibodies to a wide range of environmental proteins among which moulds are only one participant.

Hypersensitivity pneumonitis (HP) results from exaggeration of the normal IgE immune response against inhaled foreign (mould and other) proteins and is characterised by an intense immune reaction. Unlike immediate hypersensitivity, HP is not induced by normal levels of mould spores and in most cases result from occupational exposures to very large quantities of mould (or other) proteins. Uncommon allergic syndromes such as allergic bronchopulmonary aspergillosis (ABPA) and allergic fungal sinusitis (AFS) are caused by mould growing in airways or sinus cavities. These syndromes are most commonly associated with Aspergillosis and Curvularia mould colonisation, although they will only cause adverse health effects if the subject is allergic to the specific mould species that has taken up residence.


Mould elements can directly infect some tissues and cause mycotic or fungal-related pathological and inflammatory illness. Those infections in which there is deep tissue invasion are primarily restricted to the immunocompromised, although some mould species can also infect immunocompetent people. For example, acute sinusitis, although often bacterial or viral in nature, the problem of chronic sinus infections is often due to inflammation of the mucous membranes caused by mould elements. Superficial fungal infections, in contrast to serious mycotic infections are extremely common on the skin or mucosal surfaces of normal subjects. These superficial infections include infections of the feet, nails, groin, dry body skin and oral or vaginal mucosa. Some of the common organisms involved with these infections e.g. Trychophyton rubrum, can be found growing as indoor moulds.

Toxic responses:

The toxic effects from mould exposure are thought to relate to the exposure to biochemical products of mould such as mycotoxins on the surface of the mould spores rather than the growth of mould in the body. Mycotoxins are secondary metabolites produced by fungi, which can cause toxic response in animals and humans, often at very low concentrations. Species of mycotoxin-producing moulds include Furasium, Trichoderma, and Stachybotrys (American Academy of Pediatrics). The type and amount (if any) of mycotoxins produced is dependent on a complex and poorly understood interaction of specific environmental factors. However, even under the same conditions of growth, the type and quantity of mycotoxins produced by mould species can vary extensively from one isolate to another. Hence the presence of mycotoxins cannot be assumed based on the mere presence of toxigenic species.

If mycotoxins are to have human health effects, there must be an actual presence of mycotoxins, a pathway of exposure (either through ingestion, inhalation or skin contact) to a susceptible person and absorption of a toxic dose over a sufficiently short period of time. An inhalation exposure requires the generation of an aerosol of substrate, fungal fragments of spores. The effects of mycotoxins range from short-term irritation such as dermatosis to neurotoxic symptoms and cancer.

American Academy of Pediatrics - Committee on Environmental H, 1998. Toxic effects of indoor moulds. Pediatrics 101: 712-4.
Colorado Department of Public Health & Environment, 2002. Mould Information Sheet. State of Colorado.
Etzel, R.A., 2007. Indoor and outdoor air pollution: Tobacco smoke, moulds and diseases in infants and children. International Journal of Hygiene and Environmental Health 210: 611 - 616.
Genius, S.J., 2007. Review article: Clinical medicine and the budding science of indoor mould exposure. European Journal of Internal Medicine 18: 516-523.
Górny, R.L., Reponen, T., Willeke, K., Schemechel, D., Robine, E., Boissier, M. And Erinshpun, S.A., 2002. Fungal Fragments as Indoor Air Biocontaminants. Applied and Environmental Microbiology 68: 3522 - 3531.
World Health Organisation (WHO), 2009. WHO guidelines on indoor air quality: dampness and mould. World Health Organisation.