Whether lurking in the comments section of a vaping-related news story or in a beer-soaked pub conversation, most vapers will eventually encounter the piece of folk wisdom that:
inhaling anything that isn’t air isn’t good for your lungs.
We might not like it, but it does make sense.
Just like we shouldn’t set fire to some plant matter and inhale the resulting smoke, we aren’t really supposed to turn ourselves into living fog machines either. The unavoidable question is: will vaping harm our lungs in the long term?
Out of all of the touted risks of vaping – like being a gateway to smoking or cocaine, the anti-vaxxer-style idea that we should be terrified of tiny amounts of harmful chemicals, or the suggestion that they’re somehow super-addictive while patches and gums are not – this is clearly among the most plausible.
So, when it comes to e-cigarettes and the lungs, what does the evidence tell us? Is vaping better for the lungs than smoking? Does existing evidence on PG and VG tell us anything about the likely risks of vaping?
Should we be worried about the potential impact of flavouring chemicals like diacetyl and acetyl propionyl?
Here’s a look at the facts when it comes to e-cigarettes and your lungs.
What We Don’t Know
First off, it’s important to point out the information that we’re lacking. Vapers may get a little tired of frequent reminders that “we don’t have long-term evidence yet” – particularly if it’s used as an excuse for ignoring all of the things we do know – but it is often pretty relevant.
Prof. Riccardo Polosa has written a summary of the evidence on e-cigarettes and the lungs, and he points out that:
To address the potential of future disease development, hundreds of users would need to be followed for a substantial number of years before any conclusions could be made.
For vaping and the lungs, the available evidence is all short-term, so we can only speculate about the long-term risks, and there could easily be something that looks harmless in short-term studies that turns out to be very significant over time.
However, this also means that effects that look like they could lead to long-term harm may not have long-term consequences, as Dr. Michael Siegel often points out.
How Vapour Effects Cultured Cells
Even without long-term evidence on the potential risks of vaping to the lungs, researchers can look at the effects of e-liquids and e-cig vapour on human lung cells, in what are known as in vitro (which means “in glass,” i.e. cell culture) studies.
There are, however, issues with drawing firm conclusions from these studies. For example: the amount of exposure is hard to get right, researchers have an unfortunate habit of using inappropriate or unrealistic vaping setups and the cells only provide a “model” of the real situation that it’s easy to over or under-interpret the significance of.
However, there is still value in what these studies find. So far, the studies conducted on cells taken from human lungs have shown that any toxic effects on cells are related to flavouring chemicals present rather than the base mixture of PG, VG and nicotine, although nicotine was deemed to be slightly important in one of the studies.
Two of the studies found that cells exposed to e-cigarette vapour showed signs of inflammation, although another study found no such effects and also reported no sign of vapour doing damage to DNA (which could cause cancer). Cigarette smoke, in comparison, is consistently shown to be toxic to cells and also damages DNA.
The inflammation from e-cigarettes could lead to problems, but for most vapers, the fact that the effect is much less than from smoking is good news. As an example, one study directly comparing e-cigarette vapour and cigarette smoke’s effect on human bronchial (airway) cells found that after exposure to vapour, there were between 4.5 and 8 times more cells remaining than after exposure to smoke.
However, there are reasons for caution when interpreting the results of cell studies, as one example study demonstrates perfectly. This was reported to the press as showing that e-cigarettes damage lung cells, but this conclusion was brushed aside in a comically blunt fashion by Dr. Konstantinos Farsalinos.
He showed that the lowest nicotine concentration used in the study was over 500 times higher than that found in the blood of smokers, showing clear issues with interpreting the results so directly to real-world vapers.
Although cell studies have some value, presenting them with press statements making ridiculous claims about supposed findings and interpretations makes the whole issue look more like a joke. […] The publicity accompanying such studies is politics and not science.
Prof. Polosa summarizes the findings of the cell studies included in his review as follows:
Overall, despite the inconsistent and contradictory results, most acute in vitro studies are simply suggestive of non-specific irritant effects from e-vapor exposure.
What Happens to the Lungs When People Vape?
The cell studies are easier to conduct, but studies of real, living people vaping and what happens to their lungs are understandably more informative. However, there aren’t quite as many of them, and they only base their conclusions on short periods of vaping (often just 5 minutes).
In brief, the studies conducted so far have shown that short term vaping has very minor effects on the lungs, with a decrease in exhaled nitric oxide and small increases in airway resistance being the only effects uncovered to date.
Lung function is ordinarily tested by spirometry, which measures how much air a person can blow out in one second and the total amount of air he or she can expel in a single breath.
One study looking at these measures directly compared e-cigarettes and combustible cigarettes, finding that neither active nor passive vaping significantly affected lung function, whereas active (but not passive) smoking significantly reduced lung function.
Passive smoking had a greater impact than active vaping in this study (although neither were significant), and reductions in lung function have been found in other studies of second-hand smoke exposure.
But what about those studies that led to claims that e-cigarettes damage the lungs?
Generally, these studies either looked at airway resistance – literally the resistance to the flow of air through the lungs – or the amount of exhaled nitric oxide – which can be simply described as a measure of inflammation. One example study found that vaping for five minutes decreased exhaled nitric oxide by 2.1 parts per billion (or 16 percent) and increased airway resistance by 11 percent.
However, Prof. Polosa points out that these changes are “were so small and well within test variability, that it is unlikely to have any clinical relevance.”
In other words, just because the finding is statistically significant doesn’t mean that it will translate into real-world damage, and based on clinical guidelines for interpreting these tests, he assumes that they won’t. Another study did find that vaping affects exhaled nitric oxide levels about as much as smoking does, but again, the absolute changes were very small and don’t necessarily indicate long-term risk on their own.
Dr. Michael Siegel also points out that that breathing hot, humid air has a similar effect on airway resistance to vaping, showing the difficulty in extrapolating from minor effects to real-world risk. Although it must be pointed out that the air in this study was very hot (49 °C – hotter than it is in the Sahara desert!)
Although there aren’t many other studies, some evidence on asthmatic smokers suggests that switching to vaping results in improvements in spirometry readings, airway hyper-responsiveness (the easily triggered contraction of the airways that characterises asthma) and patients’ own ratings of the severity of their condition. There were only a small number of participants, but the results are encouraging, and in line with what you’d expect given the other findings above.
User surveys have also found that smokers switching to vaping see improvements in their lung function. These often rely on self-reports, though, and just because we think our lungs are improving doesn’t necessarily mean they are (although that would be in line with the other studies we’ve covered).
Other Evidence on PG and VG
Although vaping is pretty new and specific data is limited, there are some animal studies of PG and VG specifically, as well as evidence from those exposed to the fog from theatrical smoke machines, which adds some more information that may be relevant to vapers.
A study involving exposing rats to VG aerosol (which we incorrectly call “vapour”) for 2 and 13 weeks found only minimal to mild changes in the cells lining the airways for the rats, even after 13 weeks of inhalation. A similar study on PG in rats and dogs found some signs of irritation but no indication that it was toxic to the lungs, and a study from the 1940s exposed monkeys and rats to propylene glycol vapour for a year to a year and a half, finding no differences between the exposed animals and those breathing ordinary air, even after extensive examination of the lungs.
PG and VG are also added to cigarettes, and a study evaluated the impact of this by exposing rats to smoke with and without the chemicals for 13 weeks. The researchers found that their addition made no difference to the health impacts of smoking. There were obviously effects from inhaling smoke, but the PG and VG themselves made no difference.
Theatrical smoke machines also use PG, and there is some evidence on people exposed to them regularly at work. This study looked at 101 employees in relevant industries, although the fogs involved were either glycol based (like e-cig vapour) or mineral oil based.
The researchers found that glycol fogs led to coughing and dry throat (which are also reported by vapers), and that those working the closest to the source of fog had significantly reduced lung functioning, regardless of the type of fog.
Although directly vaping is different from passive exposure to smoke machines, this study shows that long-term PG exposure can have negative effects on your lungs.
Flavourings: What Diacetyl Teaches Us
Finally, there is a big unknown for vaping in the form of flavourings. We know food flavourings are safe to eat, but we don’t know whether that will also be true of inhalation. For example, diacetyl is known to cause lung damage (a condition called “popcorn lung” or bronchiolitis obliterans) when inhaled long-term, and this has been found in many e-liquids.
Reputable companies have removed diacetyl (and the similar chemical acetyl propionyl), but the lesson from diacetyl is still valid, regardless: some of the flavourings we’re inhaling could also damage our lungs in the long-term. For this issue, we really don’t know yet.
(Note: This was discussed earlier this month at the All Parliamentary Party Group on Ecigs – see here for details.)
Vaping and Your Lungs: Better Than Smoking, but Not Safe
The overall conclusion from the research so far is that vaping is almost certainly better for your lungs than smoking, which is shown by both the cell cultures and studies of real vapers.
However, vaping does have some effect on our lungs, and so it’s reasonable to expect that it could cause some problems related to persistent irritation over the long-term (although this won’t definitely be the case).
Vaping is estimated to be around 95 percent safer than smoking, but a small residual risk still probably exists, and our lungs are the most likely place for it to surface.
The take-away message is that the “don’t inhale anything that isn’t air” advice is probably right, but if the choice is between smoking and vaping, there is no question that you’ll be better off vaping.