Acute lower respiratory infections (ALRI) are the chief killer of children. Most cases are pneumonia and the majority occur among poor children under five years in developing countries. Poverty might be said to be the primary cause, which manifests as malnutrition, including micro-nutrient deficiencies, and lack of access to medical care. Another attribute of poverty is household indoor air pollution (HAP) from use of unprocessed solid fuels such as biomass (wood, animal dung and crop wastes) and coal in simple stoves. A meta-analysis of published observational studies found that young children exposed to smoke from household solid fuel use had a rate of ALRI twice that of children not exposed or where clean fuels were used. Recent studies have shown similar ALRI risks associated with short-term air pollution measurements and other indicators of exposure.