Indoor pollution is characterised by a high concentration of specific pollutants that are of indoor origin. During recent decades, concern about possible health effects resulting from indoor air pollution has increased as the concentration of indoor pollutants in modern buildings has risen to relatively higher levels. Environmental tobacco smoke and mould growth are consistently associated with asthma, but the associations between other indoor pollutants and asthma have not been confirmed.

Indoor air pollution is significant to the health of building occupants from three perspectives:

• Australians, in common with most Western populations, generally spend more than 90 per cent of their time indoors in homes, schools, offices and public buildings.
• Occupants are exposed to outdoor pollution from outdoor air that has entered the building as the result of natural air flow or ventilation systems
• Emissions from sources such as building materials and appliances can cause additional pollution of indoor air.

Environmental tobacco smoke

Environmental tobacco smoke (ETS) is probably the most important indoor pollutant, especially around young children:^{<LE III-1>}

• Smoking by either parent, particularly by the mother, increases the risk of asthma in children.^{14,15,<LE III-2>}
• The outlook for early childhood asthma is less favourable in smoking households.^{15,<LE III-2>}
• Children with asthma who are exposed to smoking in the home generally have more severe disease.^{16,<LE III-1>}
• Many adults with asthma identify ETS as a trigger for their symptoms.^{17,<LE III-1>}

Doctor-diagnosed asthma is more common among non-smoking adults exposed to ETS than those not exposed. Among people with asthma, higher ETS exposure is associated with a greater risk of severe attacks.^{18,<LE III-2>} 

Formaldehyde

Formaldehyde is an irritant to the eyes and the upper and lower respiratory tract. Symptoms are temporary and, depending upon the level and lengths of exposure, may range from burning or tingling sensations in eyes, nose and throat to chest tightness and wheezing.

• Higher formaldehyde exposure levels are more likely to result in more frequent symptoms.^{19,<LE III-2>}
• Formaldehyde causes an inflammatory response in the airways of healthy children, which may be responsible for respiratory symptoms and declines in lung function.^{20,21,<LE IV>}

Nitrogen dioxide

The major source of indoor nitrogen oxide is unflued gas appliances, wood stoves and fireplaces. As a result of tightly closed homes during winter, wood stoves and fireplaces, even when vented to the outside, may cause high concentrations of indoor air pollutants including nitrogen dioxide.^{<LE III-2>} This is likely to happen due to leaks and poor chimney design.

• High indoor nitrogen dioxide exposure causes cough, wheezing and asthma attacks. The magnitude of the effects depends on the concentration and duration of exposure.^{22,19,23,24,<LE III-2>}
• There is an association between secondary heating sources such as home fireplaces, heating stoves and kerosene heaters, and respiratory symptoms in infants.^{25,<LE III-2>}
• High exposure to nitrogen dioxide in the week before the start of a respiratory viral infection is associated with a more severe attack of asthma in children.^{19,<LE III-2>}
• Replacement of unflued gas heaters with flued gas or electric heaters is associated with significant reductions in symptoms of asthma.^{26,<LE III>}

Volatile organic compounds

Volatile organic compounds (VOCs) can cause irritation of the upper respiratory tract and airways.

• An Australian study has shown that VOC-free paint causes fewer respiratory symptoms among people with asthma than conventional acrylic paint.^{27,<LE II>}

Content Updated March 2005