Banning e-cigarettes in public spaces could be "damaging", health officials have said.
The comments from Public Health England (PHE) come after a medic at the British Medical Association's annual meeting in Belfast called for restrictions on places where e-cigarettes can be used in public.
But if such a policy was in place, it may put off smokers from using e-cigarettes to help them quit, PHE said.
Rosanna O'Connor, director of drugs, alcohol and tobacco at PHE, said: "Vaping is not the same as smoking, second-hand smoke is harmful to health but there is no evidence that e-cigarette vapour carries the same harms.
"In fact a ban on using e-cigarettes in public places could be damaging, as it may put off smokers from using e-cigarettes to help them quit. "
Dr Iain Kennedy, a consultant in public health, from Glasgow, called for restrictions on places where e-cigarettes can be used in public.
"There is growing evidence that passive vaping happens, particularly based around testing nicotine levels in households," he said.
"What we don't know yet is what the precise mechanisms of that are, what long-term harm there is. This is cutting edge research, with findings being published at the moment."
He added: "They are undoubtedly safer than cigarettes but that does not mean they are completely 100% safe.
"It looks like they are probably safe in short-term use. We don't have any evidence on long-term use because they are relatively new products.
"We always ask 'are e-cigarettes safer than cigarettes?' But I don't think taking the most harmful manmade product as the yardstick for safety is a good idea.
"It is a precautionary principle - until we do the studies and have a better idea of what the risks may or may not be, we should restrict their use in public places."
Dr Kennedy also called for a ban on the use of the chemical diacetyl in e-cigarettes.
The chemical has been linked to scarring and constriction of the tiny airways in the lungs when inhaled.
He said that the chemical, which is used to create a buttery flavour in some flavoured e-cigarettes, is "already a concern among the e-cigarette community".
His proposals were carried as a reference, which means they were noted but not made into official BMA policy.
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