The United Nations has raised concern over the damage that pollution is doing to babies developing brains.

Satellite imagery used to assess pollution levels around the world found that South Asian countries accounted for 12.2 million of the total number of affected children, but that there is also a growing problem in African cities.

The UN’s children’s agency, Unicef, says ultra-fine particles in city pollution can damage the blood-brain barrier, a delicate membrane that protects the brain from toxic substances.

Damage to the membrane has been linked to Alzheimers and Parkinson’s disease in the elderly.