One of the common attacks on vaping is that e-cigarette vapor contains formaldehyde, a small organic molecule that can be carcinogenic or even toxic in sufficient doses. Formaldehyde is everywhere. It is part of many metabolic processes, so we exhale quite a bit of it. It is used in manufacturing, so can be found in furniture and wallboard all around your home, making it a common indoor pollutant – sometimes at dangerous levels. In vapor it comes primarily from heat breaking down the larger organic molecules (mainly propylene glycol) in the liquid.
As with all chemical toxicants and carcinogens, the quantity of exposure matters. As the cliché goes, the dose makes the poison. This should be especially obvious for a molecule that is so common that we constantly exhale it. So the question for vapers is how much are they exposed to?
Not enough to worry about.
In his landmark paper on risk from vapor contaminants, Igor Burstyn, associate professor at the Drexel University School of Public Health, concluded “there is no serious concern.” This was based on the quantity of formaldehyde in vapor found by the studies available in 2014. Further studies have reinforced the conclusion. Burstyn observed that one study measured high levels of formaldehyde that seemed to be caused by contamination by subjects in a small space – that is, it was being produced by the vapers, not the vapor. In one highly publicized report he reviewed, formaldehyde and related chemicals were released only when the e-cigarettes were actually burned by the researchers (who failed to make this point clear in reporting their findings). Burstyn warned that overheating e-cigarette liquid would inevitably produce high levels of formaldehyde, as well as other harmful molecules like acrolein.
Researchers intent on generating sensationalistic headlines seem to have interpreted that as advice. In a widely criticized 2015 paper, lab researchers at Portland State University overheated e-cigarette liquid, using an unrealistic machine puffing method, and reported detecting potentially hazardous levels of formaldehyde. At the time of that publication, critics pointed out that they were measuring the chemistry of “dry puffs” which real vapers would never inhale. Just last month a team led by Konstantinos Farsalinos published a study of actual human puffing that was basically a validation study that showed the flaws of the Portland methods. It reiterated dry puff criticisms.
Most vapers occasionally experience a dry puff, the acrid vapor that results from an overheated coil or insufficient liquid flow to keep the coil cooled. But the Portland team effectively assumed that a vaper would spend all day inhaling dry puffs. In reality, a vaper will balk at the first taste of a dry puff, and is unlikely to inhale even one full puff.
Despite two years of criticism, the same research team just released a new paper that repeats their unrealistic experiments and sensationalistic conclusions.
Clive Bates published a response in PubMed Commons (basically a third-party comments section for health science papers on which previous criticisms of the Portland research have also appeared) which gets to the heart of the problem. The Portland authors attempted to justify their outlier result by suggesting that there is a legitimate disagreement about methods, which explains the wide variations in results. Bates retorts that the variation is merely between “researchers who use the products in unrealistic conditions and researchers who…measure the products in realistic conditions,” or the conditions that reflect what people really do.
Asked to comment on this dispute, Burstyn, who has not participated in the battles over the Portland research or about vaping more generally, did some calculations based on his earlier research. He first observed the chemical they found was not actually formaldehyde but a chemical that can convert to it. But even if we assume all of it is converted to formaldehyde, which he considered unlikely, and take the most extreme result from the Portland paper, it would still be difficult to exceed what is considered the acceptable daily occupational exposure to formaldehyde. His quick calculation suggests it would require vaping about 15 ml per day. Vaping that quantity of liquid is unusual, though not unheard of. But this would be 15 ml/day of nothing but dry puffs.
Burstyn reminds vapers, “it is important to remember that overheating any mixture of organic molecules is guaranteed to produce a complex mixture of compounds some of which may be hazardous.” Fortunately, overheating is a hazard that comes with its own warning.
CDC’s own guidelines about formaldehyde exposure, Burstyn notes, say that hazardous levels of formaldehyde are immediately noticeable due to “pungent, suffocating odor.” Therefore even someone with no vaping experience should realize that high levels of formaldehyde (even apart from the other unpleasant chemicals in a dry puff) are self-correcting. They would, as Burstyn puts it, cause “a reasonable person [to] protect themselves and get [their e-cigarette] to work properly.” CDC undoubtedly was not trying to endorse the message that no one would ever keep vaping the Portland dry puffs, but they effectively said as much.
Burstyn concluded that the Portland research is “smoke and crooked mirrors” designed to create unwarranted fear, and that they must have been collecting fumes in their lab that seriously stank.
Unfortunately, such scientific criticisms from both vaping proponents and outside experts are unlikely to stop bad research. PubMed Commons, like most comments sections, is generally ignored, even by the authors of the original paper. In public health, unlike in proper sciences, the fact that an analysis has shown to be fatally flawed does little or nothing to reduce its influence. Public health, and especially tobacco control, typically treat the worst outlier results found by any study — results that the rest of the literature shows are almost certainly wrong — as if they were the best available estimate. They then spin them with the most alarmist interpretation. Those who wish to restrict or denigrate e-cigarettes will inevitably continue to point to both Portland papers and claim vaping is hazardous, despite the papers being soundly debunked.