Various intervention studies aimed at improving air quality have been performed. These include: a wood stove-exchange programme, which results in an overall reduction in indoor PM2.5 concentrations; nonpolluting home heating, which reduces the level of NO2; education programmes that aim to decrease exposure to indoor allergens; displacement ventilation that may reduce CO2, formaldehyde and viable bacteria; and electrostatic air cleaners to reduce the concentration of particles of all sizes. Evaluations of the effects of interventions that aim to reduce indoor exposure should take into account the impact on health in terms of dose–response relationships.

In summary, home-based, multi-trigger, multi-component interventions with an environmental focus are effective in improving the overall quality of life and productivity of children and adolescents with asthma. Allergen-reducing interventions (i.e. installation of mechanical ventilation and heat recovery systems) result in a significant decline in asthma symptoms, such as breathlessness during exercise, wheezing, and coughing during the day and night. In addition, the installation of non-polluting heating in the homes of children with asthma significantly reduces symptoms of asthma, days off school, healthcare utilisation and visits to a pharmacist. Education and remediation to reduce exposure to both indoor allergens and environmental tobacco smoke at home reduce asthma-associated morbidity in urban children with atopic asthma.

The effectiveness of interventions in adults is uncertain, as only a small number of studies have been performed and with inconsistent results. However, one experimental study in adults suggested that office workers with airway symptoms may benefit from installation of local air cleaners. In general, increasing ventilation above currently adopted standards and guidelines is likely to improve respiratory health. Programmes and public health initiatives to reduce exposure to indoor air pollution particularly need to be adopted in low- or middle-income countries. In developing countries, use of a chimney woodstove instead of a traditional indoor open fire significantly reduces CO exposure and the risk of all respiratory symptoms.

See the entire Indoor environment Chapter