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Air Quality


Indoor Air Pollutants in Residential Settings:

Respiratory Health Effects and Remedial Measures to Minimize Exposure 


1. Background

The Lung Association commissioned a public perception survey by Environics (July 2001), which reported that the majority of Ontarians expressed the view that indoor air pollution was a relatively minor problem compared to outdoor pollution. Given that concentrations of indoor pollutants can sometimes greatly exceed outdoor concentrations, The Lung Association then commissioned a report to provide an overview of current research into the respiratory health effects of common indoor air pollutants. Prepared by Mr. Bruce M. Small, P.Eng., of Small and Fleming Limited, the report was reviewed by a panel of individuals with demonstrated expertise in the field of indoor air quality and human health. Financial support for both initiatives was provided by The Laidlaw Foundation

Each indoor contaminant was assessed individually from a respiratory health perspective. They vary widely in their nature, their potential respiratory effects, the degree of risk, the quality of evidence supporting the potential connection between exposure and health effects, and the means of remediating indoor environments to reduce or avoid exposure.

Ample evidence of respiratory risk was found to support continued action and education concerning reduction of indoor pollutants. The respiratory health risks associated with the indoor air contaminants examined include respiratory symptoms (such as rhinitis, sore throat, hoarseness, cough, phlegm, tight chest, difficult breathing and wheezing), airway irritation, respiratory infections, asthma, airway inflammation, bronchitis, emphysema, reduced lung function, idiopathic pulmonary haemorrhage, hypersensitivity pneumonitis and lung cancer.

2. Highlights

Dampness and Mould

Dampness in housing is associated with airway inflammation, exacerbation of asthma, increased incidence of wheezing and other respiratory symptoms, and increased incidence of upper respiratory infections. Excess moisture, high humidity and water leakage often lead to the growth of mould. Mould has been associated with the same list of adverse respiratory health effects as for dampness, as well as changes in lung function, e.g. increased peak flow variability, and development of allergy to mould.

Mould appears to exacerbate respiratory conditions both directly (e.g. exacerbation of existing asthma) and indirectly (e.g. increased incidence of colds and increased sensitization). Toxic mould has also been present and implicated in some cases of ideopathic pulmonary haemorrhage, but there remains some controversy over whether the evidence supports a causal connection.

Well-sealed building envelopes, proactive moisture and humidity control, and early remedial action at the first sign of water leakage or dampness in housing are the primary means of preventing subsequent mould growth and reducing the risk of respiratory effects. Complete removal of mouldy material is required once mould growth has taken place.


Bacteria can be found indoors in situations where there is water damage, dampness, or warm standing water (e.g. in humidifier trays or in the condensate from air conditioning coils). Evidence suggests an association between bacteria or bacterial endotoxin exposure in housing and increased incidence of upper respiratory infections, increased incidence of respiratory symptoms, (including cough and difficulty breathing), airway inflammation, exacerbation of asthma, chronic bronchitis, emphysema and hypersensitivity pneumonia. The environmental remedies are the same as for dampness, plus attention to standing water in humidifiers and air conditioners.


Airborne viruses can be transmitted from person to person indoors, particularly where fresh air ventilation is inadequate. Infectious organisms can be atomized by coughing, sneezing, singing and even talking. Evidence suggests adverse respiratory effects such as airway inflammation, decreased lung function and exacerbation of asthma, particularly by rhinoviruses. Development of specific childhood diseases such as measles is also cited as a risk. The spread of viruses indoors can be minimized by careful attention to personal hygiene (particularly handwashing). Fresh air ventilation can also dilute airborne viruses in the presence of infected individuals.

Dust Mites, Cockroach Antigen and Animal Dander

In addition to exacerbating asthma and decreasing lung function, dust mites may play a causative role in the development of asthma. Exposure to insects and cockroaches antigens has been also linked to exacerbation of asthma, decreased lung function and respiratory allergy. Animal dander exposure is associated with exacerbation of asthma and sensitization to the allergen.

Maintaining indoor humidity below 50% and encasement of mattresses with moisture-impermeable covers will minimize dust mite exposure. Other measures include frequent vacuuming, reduction of clutter, and if necessary, removal of carpets and drapes. Maintaining kitchen hygiene and proper housekeeping can reduce the chance of cockroach infestation. In some cases, removal of pets from the home may be necessary. If this is not practical, more frequent housekeeping and pet-free zones for allergic individuals will reduce exposure.

Environmental Tobacco Smoke (ETS)

ETS exposure is associated with a number of adverse respiratory health outcomes, including increased frequency of lower respiratory tract illnesses in infants and a reduced rate of lung function growth in childhood. In addition to exacerbation of existing asthma, ETS may also cause asthma through prenatal maternal smoking exposure. There is an increased risk of lung cancer in non-smokers who live with smokers. Cessation of all indoor smoking behaviour is the most effective way of avoiding ETS exposure in the home.

Products of Combustion

Emissions from burning wood, gas, oil, kerosene, propane and candles can result in elevated concentrations of potent contaminants including aldehydes, polycyclic aromatic hydrocarbons and carbon monoxide. Respiratory effects can include exacerbation of asthma, increased respiratory symptoms, decreased lung function, lung cancer, and in the case of carbon monoxide, death. Proper maintenance and operation of combustion appliances such as furnaces, stoves, fireplaces and heaters is essential to ensure complete fuel combustion. Adequate fresh air supply is necessary to avoid back-drafting. Installation of appropriate carbon monoxide and smoke detectors will alert occupants to combustion leakage problems. Sensitive individuals may need to consider increasing ventilation over a gas kitchen range, or replacing it with an electric range.

Products of Emission

This category includes gases (e.g. volatile organic compounds, including formaldehyde) and particles emitted from building materials, furnishings, appliances, clothing and products used in cleaning and personal hygiene. Respiratory effects include wheezing, coughing, decreased lung function, irritation of the upper respiratory tract, airway inflammation, exacerbation of asthma, increase in the risk of pneumonia in children, and, in the case of benzene, risk of lung cancer. Choosing low-emission products and ensuring adequate ventilation can reduce these pollutants.


Radon, a radioactive component of soil gas that can enter the home through cracks in basement walls and foundations, is linked strongly with lung cancer. Sealing of foundation cracks and other points of entry will reduce concentrations. Subslab ventilation is sometimes required.


Pesticides (from sprays, deodorizers, pest control strips) have been more extensively studied in the occupational environment, such as farming. In this setting, there is a potential association between some pesticide exposures and asthma. Some municipalities have enacted bylaws restricting their use outdoors. Proper indoor hygiene can reduce the need for pesticide use.

Particulate Matter

Much of the data on health effects due to particulate exposure is related to particulates and other air pollutants found outdoors. There is strong evidence linking outdoor PM10 and PM2.5 particulates to an increase in respiratory symptoms, episodes of asthma, and respiratory and cardiac mortality. Evidence suggests that there is also an association between exposure to indoor particulates and exacerbation of asthma, inflammation of the airways and increase in the allergic immune response.

Indoor air particles can be reduced by aggressive dust control programs, which may include removing curtains and carpeting. One of the most effective strategies to avoid health effects from particulates found indoors is to reduce the hazardous content of airborne and deposited household dust by following measures discussed earlier with respect to other specific indoor contaminants. Some households also maintain a "no shoes" policy to ensure that outdoor particulates from soil and road dust do not get tracked throughout a home.

3. Conclusions

While more evidence is needed to confirm all the causal links between specific indoor contaminant exposures and specific adverse respiratory health symptoms, it is still very clear that reducing unnecessary exposures from indoor contaminants can reduce the risk of negative respiratory health consequences.

Many simple and practical measures can be implemented by home occupants to improve their indoor environment, including moisture and humidity control, elimination of dampness and water leakage, mould removal, sealing of soil gas entry points, reduction of allergen exposures, cessation of smoking, proper maintenance and ventilation for combustion appliances, use of low-emission household products, aggressive dust control and adequate fresh air ventilation.

Information in the report will guide The Lung Association in further development of consumer materials in its Air Quality program. Methods of enhancing awareness of these issues among health care providers will also be explored.

The Lung Association acknowledges and thanks The Laidlaw Foundation for its generous financial support of both the Health Report and the Perception Survey.


The Lung Association wishes to acknowledge and thank the following:

  • Dr. Alan Abelsohn
  • Dr. Karen Bartlett 
  • Dr. Robert Dales 
  • Dr. Judy Leech 
  • Ian Morton
for reviewing earlier drafts of the health section of this report; and

   The Laidlaw Foundation

For its generous financial support of this initiative.