More than 95 percent of the world’s population is breathing polluted, unsafe air and the hardest hit areas are in Africa and Asia, a major study of global air pollution has found.

According to the report known as the State of Global Air and produced by the Health Effects Institute, indoor and outdoor forms of air pollution contributed to an estimated 6 million deaths worldwide in 2016—accounting for an increased risk of stroke, heart attack and lung cancer. Regions with the highest concentration of pollution include countries in North and West Africa, as well as South Asia.

The report found that China, which has instituted some measures to improve its notoriously foul air after widespread protests, has seen its air pollution exposures stabilize and even begin to slightly decline.

“There are reasons for optimism, though there is a long way to go,” Bob O’Keefe, vice-president of the institute, told The Guardian. “China seems to be now moving pretty aggressively, for instance, in cutting coal and on stronger controls. India has really begun to improve indoor air pollution through the provision of LPG [liquefied petroleum gas] as a cooking fuel, and through electrification.”