Air pollution caused the premature deaths of 600,000 children in 2016, according to a World Health Organization (WHO) report released Monday. The report found that a staggering 93 percent of people under 15 years old—some 1.8 billion children and teenagers—are breathing toxic air.

“Polluted air is poisoning millions of children and ruining their lives,” WHO director-general Tedros Adhanom Ghebreyesus said in a statement. “This is inexcusable. Every child should be able to breathe clean air so they can grow and fulfil their full potential.”

Released in advance of WHO’s first ever Global Conference on Air Pollution and Health, which will take place from October 30 to November 1 in Geneva, the report is based on global air quality measurements and rates of respiratory tract infections in children. The WHO focused on sulfates and soot particulates measuring fewer than 2.5 micrometres across, which can accumulate in human respiratory and cardiovascular systems.

These contaminants can be found in both indoor household air pollution (HAP) from building materials or fumes from cooking and heating, as well as outdoor ambient air pollution (AAP) by vehicles or industrial fossil fuel plants.

WHO estimates that seven million people prematurely die from the combined effects of HAP and AAP every year, but children are far more vulnerable because their respiratory, nervous, cardiovascular, and immune systems are still in development.

The report found that children in low-and-middle income countries are about twice as likely to be breathing toxic air than children in high-income countries. Ten percent of children who die before turning five had respiratory infections, making it second only to premature birth as the leading cause of death for this age group.

In certain regions, such as sub-Saharan Africa, acute respiratory infections are the leading cause of death for small children. Considering that pregnant women who are exposed to polluted air have a higher risk of prematurely delivering their babies, these two causes of infant mortality are deeply intertwined. “Both AAP and HAP have been linked to hypertension in pregnancy [which is] a leading cause of maternal mortality worldwide” and is “associated with adverse birth outcomes, including preterm birth and low birth weight.”

The devastating loss of life caused by air pollution can only be confronted by international cooperation and a switch to renewable energy sources, according to Maria Neira, head of the WHO's department of public health and environment.

“WHO is supporting implementation of health-wise policy measures like accelerating the switch to clean cooking and heating fuels and technologies, promoting the use of cleaner transport, energy-efficient housing and urban planning,” Neira said in a statement. “Air pollution is stunting our children’s brains, affecting their health in more ways than we suspected, but there are many straightforward ways to reduce emissions of dangerous pollutants.”