European experts weighed into the controversy about electronic cigarettes over the weekend, calling for caution.
British experts have accused the World Health Organisation of rushing to condemn the devices, putting at risk their benefits in helping smokers to quit.
But the European Respiratory Society has backed the WHO.
Researchers reported evidence that e-cigarettes can cause the same sort of damage to the body as cigarettes.
One study of laboratory mice suggested that they could trigger asthma and emphysema.
And a second study suggested evidence of changes in the lungs, similar to those caused by cigarettes.
But a third study confirmed that e-cigarettes can be used as a successful aid to quitting.
A spokesman for the society said it was opposed to e-cigarettes being unregulated.
A spokesman said: "While the short-term negative impact on health appears not as great as tobacco cigarettes, the long-term effects of e-cigarettes are not known.
"As a Society grounded in scientific principles, ERS believes that the precautionary principle should be applied when scientific evidence is inconclusive and insufficient.
"ERS agrees with the WHO proposal and believes that a strong regulatory framework is required in particular to protect children, young people and non-smokers. Furthermore, there is a clear need for more independent research to find out both potential benefits and risks of these products."
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