Around 3 billion people in the world rely on coal, wood and open-air fires for household cooking, according to the WHO's estimates. In India, 63% of the population uses such solid fuels for cooking. These fuels produce harmful pollutants such as fine particulate matter and carbon monoxide.
Country-specific data was not yet available in the report.
The WHO findings further noted that women in developing countries are more exposed to household air pollution than men.
"Poor women and children pay a hefty price from indoor air pollution since they spend more time at home breathing in smoke and soot from leaky coal and wood cook stoves," said Dr. Flavia Bustreo, WHO assistant director of General Family, Women and Child's Health in the report.
Meanwhile, outdoor air pollution killed an estimated 3.7 million people, with more than 80% of the deaths occurring in low- and middle-income countries.
The sources for ambient pollution include diesel engines and industrial emissions. Sixty percent of these deaths were due to cardiovascular diseases like stroke and heart disease.