The consensus among experts is that switching to e-cigarettes has significant health benefits for smokers, although the safety of different models might vary. There are also concerns that they might be adopted as lifestyle products by people who wouldn't otherwise have become nicotine-users, potentially becoming a 'gateway' into the use of tobacco. That doesn't appear to have happened so far, with e-cigarette use mostly confined to former or current smokers.
Safer than cigarettes, but uncertain how much safer
E-cigarettes are devices that allow users to inhale nicotine via vaporised liquid, which can be flavoured. In some cases they're refillable, and in others they're designed to be disposable.
They're often designed to look and feel like cigarettes, but they don't contain tobacco. Toxins from the burning of tobacco are the primary cause of disease and death associated with nicotine use, meaning that e-cigarettes are "almost certainly" a much safer way of inhaling nicotine according to Cancer Research UK.
Researchers at University College London (UCL) have suggested that:
"For every million smokers who switched to an e-cigarette we could expect a reduction of more than 6000 premature deaths in the UK each year, even in the event that e-cigarette use carries a significant risk of fatal diseases, and users were to continue to use them indefinitely."
They estimate the total concentration of toxins in "almost all" e-cigarettes to be below 5% of what's contained in conventional cigarettes, although the exact concentration is likely to vary by product.
Public Health England recently commissioned a review of the evidence on e-cigarettes. This found that some media reports on the dangers of e-cigarettes were "based on misinterpreted research findings", and said that the previous finding that they are 95% safer than smoking was "a reasonable estimate".
Second-hand inhalation of the vapour is also considered to be safer than second-hand inhalation of smoke, with campaigning charity Action on Smoking and Health (ASH) saying the effects on bystanders "are likely to be limited to irritation of the throat".
That said, the low concentration of toxins compared to cigarettes doesn't necessarily make them harmless. Because the technology is relatively new we don't have the same amount of information on the long-term health effects of exposure.
A 'gateway' to nicotine addiction — limited evidence so far
Aside from the health risks specifically associated with tobacco tar, the burden of being addicted to nicotine can be substantial. While using nicotine patches or e-cigarettes can prevent some of the adverse health effects of conventional cigarettes, having an addiction to nicotine is not convenient. Nor is it cheap.
There's some evidence that e-cigarettes might help smokers quit the habit, although how they compare to other products, such as nicotine patches, is not yet known.
On the other side of the equation, there are concerns that as e-cigarettes could act as a 'gateway' into nicotine addiction, particularly for children and young people.
ASH says that over 90% of 11-18 year olds in Great Britain have heard of e-cigarettes, and around 10% have tried them once or twice, but regular use among children is rare and largely confined to current or previous smokers.
Separate research in Wales has found that 6% of 10-11 year olds and 12% of 11-16 year olds have used an e-cigarette at least once, although the researchers noted that very few were regular users. This, they said, "suggests that e-cigarettes are unlikely to be making a significant direct contribution to adolescent nicotine addiction" although further research was needed to understand the relationship between the use of e-cigarettes and the use of tobacco.
Update 19 August 2015
This article has been updated to include a 2015 review of research by Public Health England, and newer figures on e-cigarette use by children and young people.
Full Fact wants to see greater accountability for public figures who mislead us—and we need your help.
Political debate in the UK is in flux right now. The UK’s exit from the European Union is approaching, we will soon have a new prime minister and potentially a general election.
We want politicians to tell the truth, and while the best politicians realise that their work should be done honestly, some aren't taking their responsibilities seriously. Both sides in the EU referendum campaign let voters down, from deceptively designed leaflets to some of the arguments made on each side. The public rightly expects more from politicians.
We want to see greater accountability for public figures who mislead. Full Fact will continue to advocate for higher standards and call out those who don't uphold them.
But we rely on the generosity of our supporters to make sure we can spot the most harmful misinformation when we most need to.
Can you help us?
Support better public debate today.