While indoor air pollution is a worldwide problem, it is especially important in developing countries, where particulate emissions from biomass fuels used for cooking and heating in confined spaces have been shown to have severe impacts on human health.

According to recent estimates in India, indoor exposures to particulates are estimated to account for more than 7% of the national burden of disease, substantially greater than that attributed to urban air pollution. A similar magnitude of health damages is observed in China. Women and young children are the primary victims of this exposure, due to prolonged periods indoors.

Indoor air pollution is caused by a variety of sources that release gases or particles into interior spaces. Air quality further deteriorates if ventilation is not sufficient, dilution with cleaner outdoor air is limited, and if additional factors such as high temperature and humidity are added. Exposure to contaminated indoor air has been identified as a significant cause of health problems affecting the poor in developing countries, especially women and younger children.

It is the relationship between meager income and the reliance on biomass energy that makes the urban and rural poor carry a disproportionately large share of heavy household indoor pollution worldwide. An estimated 2 billion people burn firewood, dung, and crop residues for heating and cooking using simple stoves and open fires, often without chimneys, flues or appropriate ventilation devices.