The number of deaths from indoor air pollution is even higher than that from all other kinds of pollutants combined.
A recent report from the UN Environment Programme says that four-point-three million people die from indoor air pollution every year, out of the seven million deaths annually caused by all kinds of atmospheric pollution.
The main cause cited was prolonged exposure to solid fuels such as coal for cooking, which can lead to respiratory conditions or heart disease.
The vast majority of deaths from household air pollution are in Southeast Asia and Africa, where people are more reliant on coal for fuel.
Experts say that airing out rooms is important,... as poor ventilation could cause pollutants to accumulate.