Researchers said teenagers who would never normally smoke were now starting out with vaping before moving on to cigarettes, risking long-term health problems.
The study by the University of California, San Francisco, found the number of schoolchildren who were smoking cigarettes and e-cigarettes - which vaporise a fluid containing nicotine and a flavouring - had risen between 2011 and 2014, suggesting that the trendy devices were a gateway to the harmful habit.
The report’s authors said youths in their study who were deemed a low risk of smoking cigarettes may not have developed a regular smoking habit if e-cigarettes did not exist.
Nicotine exposure to children as they are still growing can harm memory, attention span and emotions, according to the study published in the journal Paediatrics.
The researchers also referred to previous studies on the “gateway” effect, which suggest young people who vape are three times more likely to become smokers a year later. Senior author Dr Stanton Glantz, professor of medicine at the University of California, said: “E-cigarettes are encouraging, not discouraging, youth to smoke and to consume nicotine, and are expanding the tobacco market.”