According to WHO data, more than nine out of 10 people on the planet breathe dangerously toxic air, causing some seven million premature deaths each year.
Air pollution is especially dangerous for children, and accounts for nearly one in 10 deaths among children under five around the globe, the report found.
WHO’s study, which examined the health toll on children breathing health-hazardous levels of both outdoor and household air pollution, focused on dangerous particulate matter with a diameter of less than 2.5 micrometres (PM2.5).
These include toxins like sulfate and black carbon, which pose the greatest health risks since they can penetrate deep into the lungs or cardiovascular system.
The report found that children in poorer countries are far more at risk, with a full 98 percent of all children under five in low- and middle-income countries exposed to PM2.5 levels above WHO air quality guidelines.
That compares to 52 percent in high-income countries, WHO said.
Together, household air pollution from cooking and outdoor air pollution cause more than half of all cases of acute lower respiratory infections in young children in low- and middle-income countries, WHO said.