Brain is particularly vulnerable to the effects of tobacco during adolescence, when it rapidly matures.

Researchers have shown that young smokers, particularly boys, are more likely to suffer hearing problems, making it harder for them to focus in class.

"The levels of disruption (to hearing) are significant enough that if you were already struggling at school it could tip you towards school failure," said Dr Leslie Jacobsen, a paediatric psychiatrist at Yale University in the United States.

Dr Jacobsen looked at the effect of smoking and brain development in a group of youngsters aged between 14 and 19. The changes, found in the regions responsible for relaying signals to the ear, were greatest in the smokers, suggesting the brain is at heightened risk while maturing during adolescence, the magazine New Scientist reports.

The study added to research showing nicotine can affect brain development in the womb, said Dr Richard Todd, a child psychiatrist in the US state of Missouri.

"It seems the brain remains vulnerable long into adolescence," he was quoted as saying by Britain's Daily Mail on Thursday.

Previous research has shown toddlers whose mothers smoked during pregnancy are up to 12 times more likely to be disruptive, aggressive and withdrawn.