“In fact, exhaled aerosol is likely to increase, above background levels, the risk of disease to bystanders, especially in the case of some ENDS that produce toxicant levels in the range of that produced by some cigarettes.”
Some early studies have shown that e-cigarettes can be more effective than over-the-counter products like gum or nicotine patches.
But the report recommends preventing manufacturers from marketing e-cigs as “smoking cessation aids” until they provide robust scientific evidence to back the claim.
“Although anecdotal reports indicate that an undetermined proportion of ENDS users have quit smoking using these products, their efficacy has not been systematically evaluated yet,” the report added.
“Only a few studies have examined whether the use of ENDS is an effective method for quitting tobacco smoking.”
The WHO also advised banning sales to under-18s and said vending machines should be removed “in almost all locations.”
The report was welcomed by health officials.
Professor John Ashton of the Faculty of Public Health said: “Most adult smokers start smoking before the age of 18. That’s why many public health experts are concerned that the advertising of electronic cigarettes could make it seem normal again to think smoking is glamorous, when it is anything but.
“We also don’t know enough yet about the harms and side effects of electronic cigarettes, and it will take years before we can be sure what they are.”
However anti-smoking campaigners said that e-cigarettes were ‘considerably less-harmful’ than tobacco and warned against restricting their sale and use.
Hazel Cheeseman, director of policy and research at Action on Smoking and Health, said there was “no evidence of any harm to bystanders from use of these devices” and said regulation needed to be proportionate.
She said: “Smoking kills 100,000 people in the UK alone. Smokers who switch to using electronic cigarettes in whole or in part are likely to substantially reduce their health risks.
“Although we cannot be sure that electronic cigarettes are completely safe, as the WHO acknowledges, they are considerably less harmful than smoking tobacco and research suggests that they are already helping smokers to quit.”
The ingredients in e-cigarettes vary but they generally include nicotine and chemicals to vaporise the nicotine such as propylene glycol.
Previous studies have shown that inhaling nicotine, even without tobacco smoke, may contribute to heart disease.
Some e-cigarettes have also been found to give off formaldehyde, a known carcinogen, at higher levels than normal cigarettes. Silicate particles, a cause of lung disease, are also present in some e-cigarette vapour.
A study published last year by the Bavarian Health and Food Safety Authority found that vaping worsened indoor air quality by increasing the concentration of nicotine, particulates and aluminium.
The Department of Health is not considering banning e-cigarettes indoors but said it was planning to prohibit the sale to under 18s.
Electronic cigarettes are currently regulated as consumer products in the UK. But by 2016 they will be regulated by the Medicines and Healthcare Products Regulatory Agency.
“More and more people are using e-cigarettes and we want to make sure they are properly regulated so we can be sure of their safety,” said a Department of Health spokesman.