Scientists in China have conducted new extensive research showing air pollution could make you less intelligent.
Long term exposure to air pollution impedes individual cognitive performance, researchers found over a four year study.
Men were also found to be more at risk than women, BBC reports.
The research looked at the air pollution rate of dozens of cities in China, while monitoring the maths and verbal skills of 25,000 people in those places.
"People are having trouble with, for example, not focusing on their tasks or there's some chemistry that changes their brain and disturbs the functioning," said public health expert Xi Chen.
However, despite establishing a relationship between pollution and lower test scores, the study did not prove direct cause and effect.
While scientists previously found pollution particles damaging to the heart and lungs, evidence has shown these particles can even reach the brain, causing both physical damage and having a mental impact.
"It just adds to the weight of evidence that air pollution has a wide range of effects to your body," said professor Jonathan Grigg, a paediatrics respiratory expert.
Researchers believe the results have high global relevance, as more than 80 per cent of the world's urban population are currently breathing unsafe levels of air pollution.
Findings also showed the damage to cognitive performance was worst for people over 64.
The study concludes, "particularly on the aging brain, imply that the indirect effect on social welfare could be much larger than previously thought," Mr Xi told BBC.
Some pollutants have also been found to have a psychological impact, increasing the risk of depression.