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It’s just over a decade since e-cigarettes first hit the shelves. And since then there’s been an explosion in their popularity, with almost 3 million adults using them in Great Britain today.

But this rapid popularity, and the potential these devices hold to help people stop smoking, has left some challenges. The biggest being that research looking at their safety has struggled to keep up.

Many studies have shown that e-cigarettes appear to be far safer than smoking. But there’s still a big misconception that e-cigarettes are as harmful as smoking, and that could be stopping smokers who might benefit from switching to them.

Now a new study from a team of our scientists at UCL helps put to rest these fears. And depending on how you define ‘long-term’, the findings are the most convincing evidence to date that e-cigarettes are far safer than smoking.

E-cigarettes should be far safer than smoking

Tobacco is the world’s leading cause of preventable death, accounting for around 6 million deaths each year. That’s thanks to the cocktail of over 5,000 chemicals in cigarette smoke, of which at least 70 may cause cancer.

E-cigarettes, on the other hand, do not contain tobacco. Instead, they carry a nicotine-containing liquid which is heated into a vapour and breathed in. The nicotine satisfies the cravings associated with a smoking addiction, but doesn’t cause cancer.


Click to view full size image.

The fact that e-cigarettes don’t produce tobacco smoke and the countless chemicals found within it has always suggested that these devices should be safer than smoking. But when they first came to the market, there wasn’t enough research to be sure of this. This is why scientists around the world have sought to understand what’s in e-cigarettes and what the impact of these products might be.

Early studies looking into this showed that e-cigarette liquids, and the vapour they produce, don’t contain the same level of most toxic chemicals as tobacco cigarettes. In fact, these levels have been found to be so low that Public Health England and the Royal College of Physicians estimate that e-cigarettes are ‘around 95% safer than smoking’.

But, until now, nobody had looked at what everyday users are actually exposed to in the real-world.

So the study out today, led by Dr Lion Shahab, is the first to look at the effects of e-cigarettes in what they define as ‘long-term users’.

Just how safe are they?

The study included a group of e-cigarette users, who had been using them for an average of around 17 months, and measured the levels of nicotine and 26 potentially harmful chemicals in their body, by looking at samples of their urine and saliva.

The team compared the results to cigarette smokers, and people who both smoked and used e-cigarettes. They also looked at people who used nicotine replacement therapy (NRT), which is commonly used to help people stop smoking or as a long-term alternative.

“We looked at NRT users because we know these products are safe to use,” says Shahab. “We thought they would be a good comparison,” he adds, because long-term users get their nicotine hit from a smoke-free source, much like e-cigarette users.

Interestingly, the nicotine levels found in the samples from e-cigarette users were very similar to those who used NRT and to smokers. This suggests that people are able to satisfy their nicotine cravings through using either of these products.

The full benefit of using e-cigarettes is from completely stopping smoking

– Dr Lion Shahab, UCL

“Part of the reason why people use e-cigarettes is to stop smoking, and we have shown that they provide effective delivery of nicotine,” says Shahab.

But the key finding came when the team looked in the samples at the levels of potentially toxic chemicals. They found that there was a remarkable difference in the levels of these substances between the different groups. In fact one chemical, called NNAL (known to cause lung cancer), was 97% lower in e-cigarette users compared to smokers.

Not only did e-cigarette users have lower levels of these substances compared to smokers, but they were also found to have very similar levels to people using NRT – something that Shahab is quick to point out is known to be relatively safe.

“We have 3 decades of research into the safety of NRT, and we’ve not picked up any significant long-term health issues,” he says.

So if e-cigarettes have the same effect on the body as an established stop smoking treatment, then surely we can assume that these products are relatively ‘safe’ too? While nothing can ever be considered completely safe, we can compare it to the other things we experience in our day to day lives.

We still need to be cautious about e-cigarettes

Unfortunately, we’re not 100% convinced yet. There are a number of points left to uncover that this study hasn’t yet answered.

The first is that people who used e-cigarettes while still smoking didn’t reduce the levels of toxic chemicals they were exposed to. And a large number of e-cigarette users do still smoke.

“The full benefit of using e-cigarettes is from completely stopping smoking,” says Shahab. “Any health benefits come from dramatic reductions in these chemicals, and we’re not seeing this in people that use both e-cigarettes and combustible cigarettes.”


Dr Lion Shahab, a Cancer Research UK-funded scientists at UCL

And although this study found significantly lower levels of these substances in vapers than smokers, the chemicals are still there.

The study didn’t compare the levels of chemicals in people who don’t smoke or use  e-cigarettes with those who do, so it’s not known what the differences are likely to be. If these chemicals are found to be at higher levels in people who use the devices  there’s still a chance that some harm is being done.

According to Shahab the next step is to look for signs of damage in these different groups of people, instead of looking at levels of chemicals that cause harm. But it can take decades to see these differences.

We also know that different users use different devices and liquids. So it could be that some are safer or more harmful than others. And people also use the devices in different ways. So further work needs to be done to understand these differences, so that each vaper is using their device as safely as possible.

We intend on playing a key part in finding these answers. And that’s why we set up the UK E-Cigarette Research Forum, made up of the country’s top tobacco and e-cigarette researchers, to do exactly that.

What does this mean right now?

This study confirms that e-cigarettes are far safer than smoking. If you’re a smoker, the best thing you can do for your health is to stop. And the most effective way to do so is through free Stop Smoking Services.

And as we’ve written about previously, a number of successful quitters have managed to ditch the cigs through using both an e-cigarette and specialist support.

But this doesn’t mean that e-cigarettes are entirely without harm. If you’re a non-smoker, it’s not advisable to start vaping. We can’t yet be certain of all the long-term effects across all devices and liquids, so it’s best not to pick up the habit.

So although it’s unlikely e-cigarettes will be shown to be completely harmless (nothing ever is), today’s results are a landmark moment in showing just how much safer they are than smoking.



Shahab, L., et al. (2017). Nicotine, Carcinogen, and Toxin Exposure in Long-Term E-Cigarette and Nicotine Replacement Therapy Users. Annals of Internal Medicine. DOI: 10.7326/M16-1107


Martin Loos February 15, 2017

well on valetines day last year I told my wife I would stop smoking there and then and I would only use e cigs. Well now a year later I really did not smoke one more cigarettes. In fact I don’t like the smell anymore and I think the taste of a non flavoured tobacco with nicotine tastes better than the actual cig.

So I would recommend any smoker to give it a real try and find out about what it can do for you!

good luck, Martin

Nathan Boothby February 12, 2017

@Paul Adams. The study of diacetyl (popcorn lung) was taken out of context and relates to certain flavour concentrates. A counter study showed that this was as low as 1 100th the amount of a traditional cigarette.

A lot of studies try to put a negative view on vaporizers without comparing them to normal cigarettes and some of them even use devices outside the normal use news using a device at 5v to get it to cause a breakdown in glycerol to cause formaldehyde when the device used was not mean to be used above 3.7 – 4.2v.

We need more unbiased research that like Cancer Research UK who use study groups to accuratley gather data from the normal use of vaporizers.

I am a vape user of almost 3 years and likes ti regularly looks at studies.

Hope this helps.


Paul Adams February 12, 2017

Not trying to be awkward here but what about the evidence that some e-cigarettes contain diacetyl the cause of bronchiolitis obliterans (popcorn lung)?

Nick Peel February 9, 2017

Hi Bob,
Thanks for your comment, that’s an interesting question.
It’s unclear what may have caused the low levels of the chemicals found in the e-cigarette and NRT users, as the study didn’t look at other factors such as secondhand smoke or other possible sources of toxicants.
Best wishes,
Nick, Cancer Research UK

Nick Peel February 9, 2017

Good spot, Melek. Thanks. We’ve added in a link and the reference.
Nick, Cancer Research UK

Melek February 9, 2017

You need to link or cite the study. I feel I shouldn’t have to say this but apparently I do.

Paul February 9, 2017

I’ve been vaping for 8 years, haven’t had a cigarette for 6 years. My persistent cough is gone. I feel so much better. So whatever these studies say, I know how much my life has changed since I switched.

Bob February 9, 2017

Could the tiny levels of these dangerous chemicals detected in the ecig study group be caused by the fact that here in the USA (not sure about UK) vapors are forced into the “Smoking Area” where we are surrounded by real cigs?

stevie February 8, 2017

As mentioned when i was diagnosed with lung cancer 16 months ago, preferably you smoke reputable producers vaping liquid and not any shop corner suppliers, where you could be inhaling all sorts of other poisons into your body.

TGR February 8, 2017

Choose your poison: Inhaling vaporised liquid, many of which liquids aren’t regulated so you don’t really know what you taking, or inhale smoke? I heard something of popcorn lung being caused by vaping and we all know how bad cigarettes can be.

The act of vaping is essentially what drug users have been doing for years on end, called Chasing the dragon. Here in South Africa, there’s a substance called sugars or woonga that contains heroine and other household chemicals that’s taken in the same way as vaping. Not as fancy with the battery and element but same process none the less.Food for thought?

Andrew February 8, 2017

I managed to swap over to vaping from smoking without any problems. I’ve been vaping for about two years now and I cannot stand cigarettes now.

Emma February 7, 2017

I gave up smoking a week ago with the help of the smoking cessation team at my Drs surgery and iQuit. I have patches and used an inhaler for the first 3 days but the inhaler made me feel sick. I bought a vape epen and it’s really helped. It’s good to know that they are safer than cigarettes.

D Sussex February 7, 2017

Good to see some positive news. Look forward to the follow up.

I would take slight issue with the statement “The full benefit of using e-cigarettes is from completely stopping smoking,” Full benefit comes in many guises, including enjoying vaping for what it is in its own right, including enjoying flavours.

Smokers my still wish to smoke for the rapid nicotine hit, and also vape for other reasons.

Steven Raith February 6, 2017

“But this doesn’t mean that e-cigarettes are entirely without harm.”

Can I ask who is stating this as fact? Because I’ve never heard any e-cig user claiming this, nor any vendor. In fact, the only people who claim that e-cigs are objectively harmless as a fact (so they can point out that they are not) are those in tobacco control and public health. I’m not even joking.

What they are is *relatively* harmless compared to lit tobacco, which is not only a perfectly valid piece of objective assessment based on the evidence we have, and the materials science we know extremely well (although in a slightly backhanded way – e-cigarette use long term might be like losing the tips of all your fingers, whereas smoking is like being run over a series of articulated lorries, that are on fire, such is the massive harm smoking does) but that relative harm *is* the actual important point; as from any population level data anyone wishes to pick from, regular users of e-cigarettes are *almost entirely without exception* smokers and former smokers.

And by that I mean more than once a week, never mind at least once a day (which would be a true measure of a formed habit, rather than just toying with it) – the ‘any use in the past 30 days’ measurement used in the US is quite patently a deliberately poor measure chosen for political purposes. It’s as stupid as claiming that anyone who has had a glass of wine in the last 30 days is a functional alcoholic.

Given that we can comfortably say that almost without exception, all e-cig users are former or current smokers, then the relative harm to the vast majority of users from e-cigs is actually a *negative* harm – that is, a net benefit to their health.

As you correctly point out, chemical levels in dual users may be similar to normal smokers, but you have to look at actual changes in health; for example, I know a smoker who has one fag in the morning, and one at night, and fill in the rest of the day with an e-cig. I’m sure he’d show up as having notable levels of noxious crap in his system from those tabs, but he can now walk up quarter mile, one in three hill without getting hopelessly out of breath on the way. Twice.

That is a massive net gain to him – he has enough stamina where regular exercise is now A Thing He Can Consider, which previously he’d not have even thought of because who wants to be coughing up phlegm gems in the gym showers after a workout? So now he gyms (irregularly) and has lost a few pounds. He seems to be in a much better frame of mind and more confident, too. This is a massive benefit to him. But he’d still show ‘smoker’ levels of chemicals in his blood. Chemicals are not the whole story, not by a long shot.

Whilst I appreciate that CRUK have to be very considerate in terms of any position they take, and to be cautious with any statements to that effect, I do think it would to the Public Health community at large a world of good if they were to stop focusing entirely on statistical and chemical measurements, and actually *speak* to users of these devices and see the massive difference they make to their quality of life, and factor that into their studies and positions – and without wishing to get to morbid, I’m sure that quality of life is something CRUK would be familiar with for many of those it works with/for, and is not something that you’d discount lightly.

There is far, far more to this than just numbers and measurements and the sooner those of us who are generally on side with harm reduction can get those who are ideologically opposed to harm reduction (and that is *exactly* what it is, given the very strong evidence of the relative harms from e-cigs and lit tobacco – there is now no excuse to claim otherwise) to stop spreading their utter crap in the press – be it mendacious statistics twiddling (such as in the US, where they deliberately conflate lit tobacco – which kills – and smokeless tobacco of any kind – which quite simply, does not), or openly lying, as recently done by a senior tobacco control wonk in Australia, where it was claimed that smoking levels in the US haven’t dropped but have in fact risen.

This was on *national television*. He wasn’t corrected on it. People in Australia now think that the US has more smoking than before, despite all the evidence proving beyond any measure of doubt otherwise. And this person who shall remain nameless, will *never* get called up on this, because they work in Public Health. Who watches the watchers, etc.

There needs to be a sea change in attitude, and a root and branches rethink of our attitude towards significantly reduced harm alternatives to products that kill over a million people in the US and Western Europe alone. Every. Single. Year. And that’s before you start looking at property damage (three housefires a day – in London alone – are directly attributable to lit tobacco), pollution, etc caused by lit tobacco that either aren’t applicable to reduced risk products (I’m quite sure Snus hasn’t started any house fires, ever) or are massively reduced (The fact that battery fires related to e-cigs are newsworthy is testament to how rare they are – notice how you don’t see news stories about cigarette fires…) by these products.

That we even have to discuss, after all the evidence we have of the lack of acute harm, and the lack of any objective evidence of harm in the longest term users (who are heading towards a decade of use) whether these products are ‘safe enough’ is utterly mind-boggling.

This isn’t the 60s any more, where Big Tobacco has influence over the media and politicians, and can hide research it doesn’t like – we have Pubmed Commons, where critique is open; and the horrible, horrible irony is that the tobacco industries research is world class and open to all as they try to be whiter than white and claw back some of their reputation, and it’s the *public health research* that is being shown again and again and again to be utterly woeful, full of holes, unrealistically set up, deliberately misleading, failing to compare harm etc – yet still gets breathless front page press coverage *every* time it comes out, with no recourse for correction, even before it’s been formally peer reviewed or published in many cases!

As David Sweanor likes to recount, it’d be like if when refrigerators came out, people were finding problems like the fact that they didn’t go *quite* to 2deg C, and sometimes fluttered around 3deg C and that getting front page news (Big Elecric is lying again, remember when Edison electrocuted an elephant, he can’t be trusted!) as opposed to actually encouraging this imperfect, but damned well good enough method of food preservation – while, all the time, people are still dying of stomach cancer because of eating poorly preserved food.

That’s literally the level of debate we have on this matter at the moment regarding lit tobacco and trying to reduce the scourge it has on the health of the world, and it staggers me that This Is Even A Thing.

Steven R
Near five years a non-smoker.