Studies in India have found that in some areas, household air pollution is so high that it actually increases outdoor (ambient) air pollution - leading to pollution levels more than three times higher than a typical London street, and well above WHO-recommended safety levels.
A third of the world's population use plant-based solid fuels such as wood or charcoal, or coal, to cook, heat, and light their homes, primarily in Asia and Africa, researchers said.
These smoky, dirty fuels are often used in an open fire or simple stove, resulting in high levels of household air pollution in poorly ventilated homes.
Researchers led by Professor Stephen Gordon, from the Liverpool School of Tropical Medicine, UK, and Professor William Martin, from The Ohio State University, US, examined evidence for the effects of household air pollution on health.
They conclude that an estimated 600-800 million families worldwide are at increased risk of illnesses such as respiratory tract infections, pneumonia, COPD, asthma, and lung cancer.
Estimates suggest that household air pollution killed 3.5 to 4 million people in 2010. Although overall rates of exposure to household air pollution have been declining slowly in recent years, population growth means that the number of people exposed has remained stagnant, at around 2.8 billion people worldwide.
Despite this huge toll of premature death and ill health, coordinated international and country-led efforts to tackle household air pollution have thus far been insufficient, said researchers, and public awareness of the risks of cooking with solid fuels in poorly ventilated homes remains low in the areas most badly affected.
The women and children living in poverty who are most affected by household air pollution are also likely to have poor access to health-care - especially the complex and expensive treatments required for much of the respiratory illness and cancer caused by household air pollution.
"Although a number of clean cooking technologies – such as advanced cook stoves, LPG or solar power systems - exist, providing affected homes with cleaner ways to cook, heat, and light their homes with biomass fuel will not be the long term solution," said Gordon.
"In communities where solid fuel cooking methods are currently the norm, cleaner fuel and cooking methods need to be at least as affordable, efficient, and long-lasting as the traditional style methods they replace," Gordon added.
The study was published in The Lancet Respiratory Medicine journal.

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