Study: High Voltage and Formaldehyde Output From E-Cigs

By Lindsay Fox Posted August 1, 2014

New High Voltage and Formaldehyde Output From E-Cigarettes


There’s a simple rule that you’re not supposed to report scientific results to the media before the actual paper is released, a practice known as “science by press release.” The reason for this is pretty obvious: you report the findings but don’t provide sufficient information on your methodology or even the full data set, meaning that the conclusions are much more readily taken out of context. Unfortunately, the authors of a new paper into the carbonyl output of e-cigarettes (things like formaldehyde and acetaldehyde) and how the PG/VG ratio and voltage used influence it decided that the best way to disseminate their findings was through the New York Times.


This generated quite some discussion among vapers, as well as some initial analysis and added detail from Dr. Farsalinos, but the time between the publication of the NY Times article and the actual paper was 12 days. The headline “Some E-Cigarettes Deliver a Puff of Carcinogens” stays with the readers, but the context is not only undisclosed, it’s unavailable. However, now the full paper has been released, we can dig a little deeper and find out what the scare-stories really mean for vapers.




  • Researchers tested 10 commercially available e-liquids and 3 “control” liquids made using VG, PG/VG and PG with nicotine and some water.


  • An eGo Twist was used with clearomizers with a 2.4 ohm atomizer, with the main tests conducted at 3.4 V (4.8 W) and those addressing the impact of voltage at 3.2 V (4.3 W), 4 V (6.7 W) and 4.8 V (9.6 W).


  • In the tests on commercially-available liquids (at 3.4 V), the levels of carbonyl compounds found were drastically lower than in conventional cigarettes, with the most commonly detected being formaldehyde, acetaldehyde, acetone and butanal. Strangely, no acrolein was detected.


  • Testing of commercial e-liquids and specifically-mixed batches indicates that PG (propylene glycol) is responsible for much of the carbonyl production, and VG-only liquids generally produced lower levels. Even one liquid with PEG (polyethylene glycol) as the main component produced smaller levels of toxic chemicals.


  • The biggest increase from 3.2 to 4.8 V was observed for 50/50 PG/VG based liquid in formaldehyde content, which rose from 0.13 to 27 μg per 15 puffs (an increase of over 200 times). This, and the result for PG-based liquid, was within the range of formaldehyde content per cigarette of 1.6 to 52 μg.


  • The overall increase in formaldehyde, acetone and acetaldehyde increased by between 4 and 200 times when the voltage was increased from 3.2 to 4.8 V.


  • The main issue with the findings is that most vapers won’t use a top-coil clearomizer at 9.6 W, because it will either result in “dry puffs” or at very least a “dulled” flavor most vapers will not enjoy. Such powers may be common for dripping, but not for basic clearomizers. This can be easily tested at home with a clearomizer and VV/VW device – try it out and see if you’d vape like that.


  • Even if the formaldehyde levels found in the worst-case scenarios were experienced by vapers everyday, this is just one carcinogen out of around 70 in tobacco smoke: the reduction in risk associated with vaping is still notable.


What They Did – PG/VG Ratio and Variable Voltage Testing

The basic aim of the study was to provide a little more information about how the characteristics of the liquids used and the devices themselves affect the chemistry of e-cig vapor. Most research conducted on the topic has looked at “cig-a-like,” first-generation models, whereas the vast majority of vapers use eGo-style or “mod” e-cigarettes. The biggest difference in terms of hardware is the level of control vapers have over the power going to the atomizer in higher-end devices. Additionally, the varying PG/VG ratios liquids are available in likely have a role to play, because it’s their thermal decomposition that produces the lighter, more toxic carbonyls like formaldehyde, acrolein, acetaldehyde and acetone.


The researchers used a variable-voltage eGo style battery and a standard, top-coil clearomizer for the testing, both of which were popular in Poland and obtained online. The clearomizer had a resistance of 2.4 ohms, and the main set of tests was conducted with the batteries set to 3.4 volts. The batteries were charged before each test, and replaced with a new battery when the charge level dropped below 50 percent.


They tested ten different liquids, in addition to three “control” solutions made without flavorings. The 10 commercial liquids were primarily tobacco-flavored options (with “Sunny Banana” being the only obviously non-tobacco liquid, and also the only one in 24 mg/ml), with varying PG/VG ratios and some reporting more ingredients than others. The control liquids were made with small amounts of nicotine, water, and then either PG, VG or a 50/50 mix of both. In addition to the main tests on the commercial liquids, nine combinations of voltages (3.2, 4 and 4.8 volts) and the three control liquids were used to investigate the impact of voltage and base composition on carbonyl production.


The vaping was done by a smoking machine, which took 15 puffs of 1.8 seconds in length (a volume of 70 ml) with an inter-puff interval of 17 seconds; roughly speaking, a 2-second puff every 20 seconds. The batteries were manual, so were activated by a researcher one second before the machine took a puff and released it as soon as it was finished. Each device was used for two testing runs, with a five minute interval between them.


PG-Based Liquids Produce More Carbonyls Than VG-Based Liquids


For the ten general-sale liquids, the tests were all conducted at 3.4 volts, and the results show that vapers under these conditions are exposed to only very small levels of toxic chemicals. The highest quantities found of these two chemicals were 59 nanograms (billionths of a gram) per 15 puffs (taken as “one cigarette” of usage) for formaldehyde, and 107 ng per 15 puffs for acetaldehyde. The lower end for cigarettes has been quoted (in previous research by the same authors) 1.6 μg (millionths of a gram: so this is equal to 1,600 ng) per cigarette for formaldehyde and 52 μg (52,000 ng) per cig for acetaldehyde. This is a comparison between the worst-case findings for e-cigs and the best-case findings for cigarettes, and the conclusion is unavoidable: e-cigarettes drastically reduce exposure to toxic chemicals.


There was at least one carbonyl in each liquid tested, but the most common were formaldehyde, acetaldehyde, acetone and butanal. Acrolein wasn’t detected in any of the samples, and many of the remaining chemicals were only found in quantities big enough to actually measure on rare occasions. For instance, crotonaldehyde was only found in one e-liquid and benzaldehyde only in three. Generally speaking, VG-based liquids have lower levels of and fewer detectable carbonyls. Interestingly, one liquid which included 40 percent PEG (polyethylene glycol) only had butanal present, with all other chemicals either not detected or below the limit of measurement.


The experimentation with different voltages and the flavor-free e-liquids created the headline findings, though. The researchers looked at formaldehyde, acetaldehyde and acetone content after 15 puffs at various voltages, for PG, PG/VG and VG liquids. The graphs show pretty clearly, as would be expected because more power is delivered, that larger voltages generally increase the quantities of these chemicals. However, the only statistically significant increases (meaning those where it’s possible to rule out chance variation with reasonable confidence) were obtained in the tests at 4.8 volts. Formaldehyde and acetaldehyde were found in quantities that averaged between 13 and 807 times lower than those found in a conventional cigarette at the lower voltages (all apart from 4.8 V).


The most dramatic change was in formaldehyde content, which (for the PG/VG liquid) increased from 0.13 to 27 μg. This liquid had the biggest change observed, the PG-only one went from 0.53 to 17.6 μg and the VG-only one went from 0.02 to 0.15 μg per 15 puffs. It appears from this that PG, as suspected, is the main cause of the formaldehyde detected in e-cigarettes, and the same basic theme extends to acetaldehyde and acetone. However, the mixed PG/VG base produced more acetone than the PG-only mixture, and the only statistically significant increase in acetaldehyde production between 3.2 V and 4.8 V was for the VG liquid, which rose from 0.17 μg to 1.24 μg per 15 puffs. Generally, the level of formaldehyde, acetaldehyde and acetone increased by between 4 to 200 times as the voltage was pushed from 3.2 to 4.8 V.


What it Means: Unrealistic Vaping Conditions Produce More Toxic Components


The headlines relating to this study invariably focus on the fact that the level of formaldehyde produced by 15 puffs of the PG or PG/VG based liquids tested at 4.8 V was within the per-cigarette range of 1.6 to 52 μg. It’s important to note that (although the numerical values weren’t provided) the graph shows that there was very little increase when the voltage was changed to 4 volts, so it’s only in the very high voltage condition where the levels rose to cigarette-like levels. Since the value found for the PG/VG liquid was comfortably within the range, the authors point out that at 4.8 V, vaping could even expose users to more formaldehyde than smoking.


This is the controversial suggestion touted in the press before even the resistance of the atomizer was known. Now we know it was 2.4 ohms, the wattages for each of the tests can be determined. At 3.4 V (used for the tests of the commercial liquids), the power was 4.8 watts, at 3.2 V it’s around 4.3 W, at 4 V it’s around 6.7 W and at 4.8 V it’s 9.6 W. Remember that 9.6 W was the only power where large increases in formaldehyde were observed, and that the researchers used a top-coil clearomizer puffed for around 2 seconds every 20 seconds.


Firstly, research from Dr. Farsalinos (which the authors were well aware of) suggests a 4 second puff with an interval of 20 to 30 seconds between puffs for such studies, based on observations of vapers. This is a limitation of the design which the authors didn’t really justify and may have impacted on how well the results generalize to real-world use. However, the shorter interval between puffs was accompanied with a smaller puff length, so it could be quite a minor factor.


The bigger problem is the idea that many people actually would use a standard top-coil clearomizer at 9.6 W. I tested this out, and found that based on a few different juices pushing the power up to 9.5 W at best was noticeably detrimental to flavor and at worst anything from unpleasant to un-vape-able. Take those same e-liquids down to 7 W (where the formalehyde levels were much lower) and the flavors come through much more clearly without that unpleasant, borderline eye-watering undercurrent. If you’re dripping on a rebuildable atomizer, you may go up to 9.5 W and beyond with no issues, but on a basic clearomizer it doesn’t seem like real-world usage, particularly given that many clearomizer users will often be using an eGo-type device without voltage control. Dr. Farsalinos comments that in a recent study he performed, many vapers couldn’t use a Vivi Nova when set to 10 W because of dry puffs, in line with what anybody with a clearomizer and a VV/VW device can verify for themselves: it doesn’t taste pleasant if your power is too high!


However, even in that unrealistic scenario, there is still a clear point to be made: so what? Of course it’s not ideal that formaldehyde was detected in cigarette-like quantities, but formaldehyde is far from the only chemical of concern in cigarette smoke. So even if this was what all vapers did, would it really be that big a deal that one out of the 70 carcinogens or so in cigarette smoke was present in the same quantities in e-cig vapor? It still seems like a pretty significant reduction in risk, and it wouldn’t be hard for vapers to substitute VG-based liquids if that was how most users vape. Thankfully, it isn’t, but switching to VG is still an option if really want to reduce your risk as much as possible.




So, if you like it when you send too much power to your clearomizer, receive dry puffs and ruin the flavor of your e-liquid, you may be exposed to one chemical in cigarette-like quantities. But if you’re a normal vaper, it’s hard to imagine that this finding really means anything other than that under ordinary usage conditions, the levels of toxic components in e-cigs are much lower than those in tobacco cigarettes. The only difference between this and the numerous other studies which have made the same basic finding is that the authors decided to let the press peek at the most shocking parts before anybody knew the most integral pieces of information like the resistance of the atomizer. When this was disclosed, the problem was obvious to anybody who’s vaped from a clearomizer, or who knows anything about the vaping habits of clearomizer users.


How could researchers avoid this obvious problem in future? How about actually having somebody there to try it? Would it be such a challenge to have a vaper going through the puffing protocol too, pointing out when the device is becoming unusable, tasting disgusting or otherwise becoming something they wouldn’t use? Or even just having a puff after the machine’s series of puffs is over? This will undoubtedly be addressed in future research, but it seems shocking that such a basic additional test is so routinely not conducted. If the formaldehyde levels rise before we can tell, then there may be a small issue, but if it’s only produced with “dry” puffs, then I strongly doubt any vaper is being exposed to similar levels for anything more than a puff or two.