Teenagers who have used e-cigarettes are between three and five times more likely to start smoking compared to those who never used them, according to a new report.

A report by the Health Research Board also shows more than one in five 12 to 17-year-olds have used e-cigarettes, even though their main purpose is to help people quit.

Dr Jean Long, Head of the Evidence Centre at the Health Research Board, says e-cigarettes are not harmless products and there are a number of acute effects including poisonings and burns, blast injuries, lung injuries and exacerbation of asthma, while the long-term effects of e-cigarettes, beyond 24 months, is unknown.

Speaking to RTÉ's Morning Ireland, Dr Long said she does not know how children as young as 12 are able to buy e-cigarettes but understands that these products are not properly regulated in retail outlets.

She said it would "be very useful" if legislation to ban the sale of these cigarettes to those under the age of 18 was progressed further.

Dr Long said in some very small, short time period studies, e-cigarettes have been found to be "slightly less harmful than cigarettes" but no one knows their effects beyond 24 months and no one can say they are safe beyond this time period.

She added that e-cigarettes are no more effective than approved and regulated nicotine replacement therapies to help people stop smoking.

Read HRB report in full