Air pollution has countless victims—nearly nine out of ten people across the globe breathe polluted air, according to the World Health Organization – and new research from London suggests it even reaches the unborn, moving from a mothers’ lungs to placenta and foetus.

While the toll breathing polluted air exacts on health and physical well-being is well documented and well-known, lesser known is its impact on human intelligence.

In the first study of its kind, we found continued exposure to air pollution lowers human intelligence, with the effects becoming more pronounced with age. The research was conducted with colleagues Xin Zhang of Beijing Normal University, and Xi Chen of Yale School of public Health.

In developing countries, which top the list of world’s most polluted cities, this translates into not only significant health and economic costs, but also human development costs.

India, home to six of the top ten polluted cities in the world, has struggled in recent years to curb pollution in its capital city, New Delhi, and neighboring states. Every year, the air pollution worsens during late fall and early winter, coinciding with the crop burning season, and turning it into a more permanent rather than a transient feature of city life.