Researchers believe child mortality from asthma, which already claims approximately 250,000 lives every year, is expected to increase as urban air quality continues to deteriorate across the world.

While experts aren’t completely sure what causes asthma, they do know that risk factors for developing the disease include exposure to allergens, chemical irritants, and air pollution.

The level of that last item on the list has been rising at an “alarming” rate, according to The Guardian, particularly in cities in developing countries, which are also less likely to have access to comprehensive medical care for all the children who will be affected by the growing air pollution. Or, as Flavia Bustreo, the WHO assistant director general, was quoted as saying,

As urban air quality declines, the risk of stroke, heart disease, lung cancer, and chronic and acute respiratory diseases, including asthma, increases for the people who live in them. When dirty air blankets our cities the most vulnerable urban populations – the youngest, oldest and poorest – are the most impacted.