Mould and School Indoor Air Quality

Mould and School Indoor Air Quality

This document is intended for school administrators, staff, parents, students, and anyone concerned with mould problems in schools. Indoor mould overgrowth can be a common problem in schools, often with serious health concerns.

Some individuals are more sensitive to mould exposure than others. Whether the individual has a true allergy or has a sensitivity to mould, very low exposure levels can cause mild to severe symptoms.

According to Health Canada “Responses to inhalation may be mild and non-observable, may be acute and severe with flu-like symptoms, may cause irreversible change in lung functions after continuous chronic exposure, or may cause death.”[i]

Moulds can adversely affect the health of non-allergic individuals. If the indoor mould growth is not removed, healthy individuals can develop mould sensitivity to even the more benign varieties.

Whether indoor moulds are toxic or are more benign varieties, if you can see mould or “If there is mouldy odour in any indoor space, that is sufficient indication that mould is present, and that remediation should be done without regard to the kind of mould present.” (Dr. Harriet Burge, Harvard University School of Public Health.)[ii]

About Mould, or Mold

The words “mold” and “mould” are used interchangeably. “Mould” is the Canadian and British spelling and “mold” is the American.

There are three basic classifications of mould related health concerns: infectious, allergenic, and toxic. Allergic reactions are the most common and can include the following symptoms: watery eyes, runny nose, itching, rashes, hives, nasal congestion, coughing, wheezing, breathing difficulties, headache, dizziness, fatigue and in extreme cases tremors. Even the benign mould varieties will cause an allergic reaction after repeated exposures, and the reactions may become more severe over time. Mould is a known irritant to asthma sufferers.

Unlike humans who digest their foods inside the body, moulds digest their food outside the body. The “digestion” products are sometimes called “natural volatile organic compounds.” Toxic mould produces mycotoxins that can damage a variety of organs and tissues in the human body including the liver, central nervous system, lungs, digestive tract, and immune functions. Some of the symptoms related to toxic mould exposure can be dizziness, fatigue, tremors, headaches, body bruising, nosebleeds, mood swings, depression, breathing difficulties, and a weakened immune system.

The mould Stachybotrys chartarum (or atra), for example, produces the toxin trichothecene satratoxin H which attacks the respiratory system to produce coughing, congestion and bleeding of the lungs, and can lead to death. This mould is black and sticky and is found in damp environments such as on frames or sills of windows with condensation problems. Other moulds which produce harmful toxins include some strains of the following species: Acremonium, Alternaria, Aspergillus, Fusarium, Penicillum, Trichoderma, and Trichothecium.

A few fungi can invade living cells and cause infectious diseases. Two such types of fungi are Aspergillus and Fusarium. Most infectious diseases caused by fungi occur to individuals who are immune-compromised like those with severe burns, AIDS, those hospitalized for cancer treatment and those individuals who have lung diseases.

Examples of Toxic Mould

Alternaria sp. – It is often found in carpets, textiles, and on window frames. It has been associated with hypersensitivity pneumonitis. Alternaria alternata is capable of producing mycotoxins which can be related to asthma attacks, bronchiospasms, and pulmonary emphysema.

Aspergillis veriscolor – It is commonly found in soil, hay, cotton, dust, and dairy products. It can produce the mycotoxin sterigmatocystin and cyclopiaxonic acid. These toxins can cause diarrhea and upset stomach, eye, nose, and throat irritation, respiratory irritation, headaches, and fatigue. It is reported to be a liver and kidney carcinogen.

Penicillium aurantiogriseum and Penicillium brevicompactum – They can be found on paint, in soil, decaying plants, foods, and textiles. These two types of Penicillium release mycotoxins into the air. Pencillium spores may cause hypersensitivity pneumonitis, allergic skin reactions, headaches, itchy eyes, and asthma attacks.

Stachybotrys chartarum – It is found in wet building materials with high cellulose content and a low nitrogen content. This mould can produce trichothecene mycotoxins which can be responsible for cold and flu symptoms, sore throats, diarrhea, headaches, fatigue, dermatitis, memory loss, asthma attacks, respiratory problems, and tremors. The toxins produced by this fungus will suppress the immune system. It has been known to kill hogs and cattle. It has also been blamed for the death of several infants. The dead spores are still allergenic and toxigenic when inhaled.

Trichoderma sp. – It is found in soil, dead trees, paper, and pine needles, but can often be found on window ledges. It produces antibiotics which are toxic to humans.

Mould Removal

The most effective way to control moulds is to eliminate moisture, repair leaks, remove damaged or contaminated plaster, wood, etc., and clean the remaining hard surfaces. Increased ventilation can also assist in discouraging renewed mould growth by drying surfaces and limiting dampness from condensation.

When dealing with mould removal, experts recommend using the safe work practices similar to those used for the removal of asbestos. Persons removing moulds should be healthy and free of symptoms. Isolation of the work area, protection of workers and others, and thorough clean-up afterward are essential. If the mould growth is extensive, it may be wise to hire a professional abatement company. See the guidelines listed below for more detailed information.

Antimicrobial Chemical Treatments

CAUTION: Chemical Sprays that coat surfaces and are said to inhibit further mould growth are usually an unnecessary expense, are of questionable value, and are not recommended by the most reputable sources (see below). There is also a risk that people may be tempted to cut corners by trying these antimicrobial treatments when remedial work is what is really needed.

Testing for Moulds

Caution: Air quality testing is sometimes used to determine the existence of or the extent of contaminants. Tests for mould infestation may help indicate the degree of growth and the varieties present, but tests need to be used with caution for several reasons.

Testing can be expensive and collection of spore information can be unreliable. Also, the raw data can be misinterpreted by the untrained. Mould testing can be valuable to a qualified building evaluator, but may not be a necessary expense in most cases. Professionals in building environments rely on much more than raw test results to evaluate what is usually a complex situation.

If an air quality test does not find mould in a building, this is not a guarantee that mould overgrowth is not present. Common mould tests measure live spores. If the colony is in a dormant part of the life cycle, live spores will not be in production, or may not be found in numbers that reflect the actual colony. If the moisture levels are down, or if air circulation is up, or if any of several other factors are present or absent, the tests may not find mould even though mould contamination may still be present. This is an oversimplification, but a very important point. It is also now recognized that mould particles in the air, dead mould not measured by most tests, contain mould cells that can cause health reactions. It is essential, when releasing mould test data, that a clear interpretation by a qualified professional accompany the data.

Although mould testing is expensive and of questionable value, when considering mould test results, the following occurrences indicate possible concern:

  • mould species that are not found in the building’s outdoor samples, but are found in the building’s indoor samples,
  • moulds that produce mycotoxins are found indoors,
  • high spore counts
  • spore counts that are higher indoors than outdoors.

Testing to identify the types of mould present is not common these days because it is recognized that indoor mould of any kind is not good for people, and as one occupational hygienist put it, “If you can see or smell mould then you have mould, so find it and get rid of it.”

Access to Information

Who has access to test results and their interpretations?

We understand that in most of Canada, test reports are restricted to government and school officials, to staff, and to parents of school children who may be affected, and are not normally made available to third parties or the public. Unfortunately, some school boards still exclude parents and only provide test results to staff serving on Joint Occupational Health and Safety Committees. Access limitations are often intended to protect privacy concerns, however parents of children in the school in question are legally entitled to have exposure data. These parents of children potentially affected should also be supplied with the interpretation of the expert who evaluated the site – very important information because it is too easy for non-experts to misinterpret test results.

For more information

Health Canada’s guidelines:

AIHA Facts About Mold:

Canadian Construction Association, Mould Guidelines:

“Guidelines on Assessment and Remediation of Fungi in Indoor Environments” (otherwise known as “the New York Protocol”) advises against antimicrobial use. For instruction on antimicrobial treatments, see page 9 of the executive summary on

Mould Remediation in Schools and Commercial Buildings:

NIOSH alert: Preventing Occupational Respiratory Disease from Exposures Caused by Dampness in Office Buildings, Schools, and Other Nonindustrial Buildings. Centers for Disease Control and Prevention. November, 2012.


Health Canada’s guidelines:

AIHA Facts About Mold:

Canadian Construction Association, Mould Guidelines:

Guidelines on Assessment and Remediation of Fungi in Indoor Environments, New York:

Mould Remediation in Schools and Commercial Buildings:

Miller JD, McMullin DR., Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. PubMed 2014 Nov 4.

  1. Mudarri and W. J. Fisk, Public health and economic impact of dampness and mold. Indoor Air 2007; 17: 226–235

NIOSH alert: Preventing Occupational Respiratory Disease from Exposures Caused by Dampness in Office Buildings, Schools, and Other Nonindustrial Buildings. Centers for Disease Control and Prevention. November, 2012.

“Airborne Fungal Glossary”, University of Minnesota.

Indoor Air Quality in Schools. Cutter Information Corporation, 1996.

[i] Significance of Fungi in Indoor Air, Health Canada, p.S9, 1987

[ii] Personal communication, Dr. Harriet Burge, Harvard University School of Public Health

[1] Significance of Fungi in Indoor Air, Health Canada, p.S9, 1987

[1] Personal communication, Dr. Harriet Burge, Harvard University School of Public Health