"Menthol stimulates the cooling receptors in the lung and oral pharynx," said Professor Gregory Connolly Howard of the Harvard School of Public Health (HSPH), co-author of the paper.

"It makes smoking easier."

Menthol appears as an additive in around 90% of cigarettes manufactured in the US -- but only a third of these brands are explicitly marketed as mentholated.

"For decades, the tobacco industry has carefully manipulated menthol content not only to lure youth but also to lock in lifelong adult customers," said co-author Professor Howard Koh, associate dean of Public Health Practice at HSPH.

Yet the tobacco industry denies that there is any strategy to deliberately hook young smokers.

"There is very little direct relevant data that shows menthol affects initiation," said David Sylvia, a spokesperson for Philip Morris, makers of Marlboro amongst others.

Sylvia was adamant that their products 'were not designed for nor marketed to underage smokers.'

The study also looked at the ethnicity of adult smokers -- they found that African Americans were more likely to smoke menthol cigarettes than any other group.

"This is another example of the cynical behaviour of the tobacco industry to hook teens and African Americans to a deadly addiction," said Professor Connolly.

"This is after the industry told the American public it had changed its marketing practices."

A bill currently before Congress would give the US Food & Drug Administration (FDA) powers to regulate additives such as menthol -- at present, they have no authority to act.

"The FDA bill provides the vehicle to end the hypocrisy and save the lives of the young and a targeted minority group," Professor Connolly said.