The smog enveloping many of the world’s largest cities, like Delhi, India, and Beijing, China, has triggered widespread unrest from residents who demand cleaner air.

But the citizens most affected aren’t able to advocate — that’s because they’re babies whose brains are being exposed to hazardous chemicals.

Worldwide, roughly 17 million babies are breathing toxic air that complicates natural brain development, according to a recent report by UNICEF. About two thirds of these babies live in South Asian countries that have been contending with severe air pollution crises.

Each year, more than 2 billion children are exposed to toxic air pollution. That smog is also affecting the health of unborn babies, according to another recent study in the medical journal BMJ that analyzed the health of newborns in the UK.

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“Though the new results from the UK are concerning, a global perspective reveals something approaching a public health catastrophe,” researchers wrote in a BMJ editorial, noting that similar research has not been conducted in “extreme exposure environments like Delhi.

“There is an urgent need to turn attention to such environments where large numbers are at considerable risk of harm,” they continued.

Babies, in particular, have a higher risk for air pollution-related health problems than adults because their brains are more susceptible to toxins, they take more breaths, and their immune systems are less developed, UNICEF reported.

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Even children who experience normal brain development face consequences from breathing toxic air.

“When children get sick, they might miss school, further limiting their learning and development potential,” Unicef said in its report.

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UNICEF warns that toxic smog exposure will only increase unless governments, businesses, and individuals resist the causes of air pollution by using more renewable energy sources, limiting the use of fossil fuels and reducing carbon emissions.

Global Citizen campaigns on reducing pollution and ensuring the health and wellbeing of children around the world. You can take action here.