Cinnamon, apple, unicorn milk - their names sound innocuous, but a respiratory specialist is warning of the dangerous toxins lurking in e-cigarettes.

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Dr Stuart Jones, the medical director of the Asthma and Respiratory Foundation, had cast doubt on claims relating to the harm they could cause relative to other cigarettes.

His warning has come ahead of a law change to be considered next year relating to how vapes are flavoured and marketed.

Dr Jones said the science around vaping has developed dramatically in the last couple of years and there were a number of animal and human studies demonstrating the harm which vaping could cause.

"Vaping causes inflammation in the airway, it damages the structure of the airway cells and the proteins.

"It affects how the immune system within the lungs will function and it potentially does have an effect on reducing lung function over time."

Dr Jones said all of those effects were, on the whole, less than those seen with conventional tobacco smoking, but he was very concerned that people believed vaping as a very low risk activity when it was not.

He said the chemical changes which occur in some vape flavourings when they are heated could also produce toxins, such as formaldehyde.

"We know from studies published this year that these substances then cause damage to human airway cells.

"There was a nice little study that showed there were about 17 protein damages that both cigarettes and e-cigarettes share. There were about 100 that only cigarettes produce and almost 120 that only vaping produced, in terms of damage to the airways."

Dr Jones said another study of 200 vape users, showed their lung function decreased by 5 percent in two years, a rate of decline between three and five times the normal loss of such functioning.

He said that showed vapes were not the safe devices people imagine them to be.

Dr Jones also had in his sights a cabinet paper on proposed changes to the Smokefree Environments Act, which claimed e-cigarettes were 95 percent less harmful than conventional tobacco.

He said that figure came from a study five years ago conducted by self-appointed experts including two who had been involved with vaping companies.

"They rated the relative harm of nicotine containing products from patches right up to vaping and they based it on the fact that vaping had less of the known carcinogens of cigarette smoking and that's [how] they came out with this claim.

"But it's very weak evidence and it's evidence that isn't actually accepted in the respiratory circles at all, though it's been embraced [in other quarters] so widely."

Dr Jones would be backing the government's targeting of some vape flavours, saying their dangers were two-fold.

"Some of the flavourings actually do create more toxic metabolites. Things like cinnamon, apple has been shown to, some of the chocolates can too and some of the berries can add to inflammation of the airways.

"But the big thing with the flavours is often they are produced and targeted to look attractive, something you'd want to try, custard vanilla cream, gummy bear or bubble gum, unicorn milk."

Dr Jones said that was similar to the tricks liquor companies use when marketing alco-pops to younger drinkers.

Ben Youdan, strategic lead for ASH has studied vaping habits of 14 and 15-year-olds.

"Young people are using vaping as a way to get out of smoking, much like adults are," he said.

"If kids are taking up vaping instead of smoking then potentially it's got a protective factor against them taking up a much more harmful option which is traditional smoking."

In New Zealand, Mr Youdan said there were about 600,000 smokers, of which 200,000 vape.

More than half of them are believed to be ex smokers, and under a third of them were people who were smoking and vaping at the same time trying to get rid of traditional cigarettes.

"E-cigarettes aren't entirely risk free, however, they are substantially less harmful than cigarettes."

The law change to be introduced next year would impose restrictions on flavoured and coloured vapes aimed at children and young people.

It would also change the way in which vaping products could be displayed in retail stores.