Nearly 17 million babies under the age of one are living in places where air pollution is "at least six times higher" than international limits, according to the United Nations Children's Fund (UNICEF).
Its report, "Danger in the air: How air pollution can affect brain development in young children," states that breathing in particulate air pollution can both undermine cognitive development and damage brain tissue.
In a statement Wednesday, UNICEF said that satellite imagery showed South Asia was home to the biggest proportion of babies — 12.2 million — living in the worst-affected areas.
The international limits relating to air pollution are set by the World Health Organization (WHO).
UNICEF's paper added that ultrafine pollution particles posed "an especially high risk" as they could more easily enter into the bloodstream and then travel through the body to the brain.
"Not only do pollutants harm babies' developing lungs, they can permanently damage their developing brains, and thus, their futures," Anthony Lake, UNICEF's executive director, said.
"Protecting children from air pollution not only benefits children," Lake added. "It … also benefits their societies — realized in reduced healthcare costs, increased productivity and a safer, cleaner environment for everyone."
The report sets out a range of ways that the impact of air pollution on babies' brains could be lowered.
These include investing in renewable sources of energy to cut air pollution, increasing the amount of green spaces in urban areas, and improving both knowledge and monitoring of air pollution.
The World Health Organization describes air pollution as a "major environmental risk to health." It says that in 2012, outdoor air pollution in cities and rural areas was caused an estimated 3 million premature deaths globally.