About 70% of all babies under a year old, whose brains are at risk because of air pollution six times the safe limit, live in South Asia, a Unicef report said on Wednesday.

The number of such babies worldwide is about 17 million. Over 12.2 million of them are in South Asia, the report, titled “Danger in the Air” said.

“Not only do pollutants harm babies’ developing lungs – they can permanently damage their developing brains – and, thus, their futures,” said Unicef Executive Director Anthony Lake.

Air pollution levels above the World Health Organization’s recommended limits is potentially harmful for children. Unicef emphasised that brain development in the first 1,000 days of a child’s life is critical.

The Unicef report comes while New Delhi, the world’s most polluted Capital city, and its surrounding areas regularly find their air quality moving into very severe and hazardous zones.

The United Nations declared Tuesday the world’s first International Smog Day. December 5 marks the anniversary of the Great Smog of London in 1952, which killed over 10,000 people directly or indirectly as a result of air pollution.

In New Delhi, the air quality was in the “very poor” quality on Tuesday, with the Central Pollution Control Board’s index recording an air quality index of 378. An AQI higher than 400 is classified as “severe”.

The index improved on Wednesday morning to 311. The air quality remained “severe” in Ghaziabad and Agra.