E-liquids are made using 4 main ingredients: vegetable glycerin (VG), propylene glycol (PG), nicotine, and food/pharmaceutical grade flavourings. Diketones such as diacetyl, acetoin and acetyl propionyl are present in a number of these flavourings as they add an authentic buttery and creamy taste to the e-liquids produced by many manufacturers.
There has been a lot of publicity about the presence of diacetyl in vape juice. The media has even gone so far as to nickname the associated medical condition, bronchiolitis obliterans, “Popcorn Lung”. Bronchiolitis obliterans has been so dubbed “Popcorn Lung” because of the prevalence of cases that have come up in workers at popular microwave popcorn factories around the world. During an investigation, the diacetyl exposure was attributed to vapour coming off large heated mixing tanks containing soybean oil, salt and flavourings, meaning factory workers would be consistently exposed to diacetyl vapour at 18 parts per million during each of their shifts.This averaged at 8 hours of exposure per shift. Another crucial aspect of this investigation is the proximity of these workers to the mixing tanks. Of the 8 patients recorded, 4 were mixers dealing directly with the mixing tanks and 4 were “microwave-packaging workers,” who worked within 30m of the mixing tanks. Notably, the workers working over 30m away did not exhibit any symptoms of bronchiolitis obliterans.
So what exactly is bronchiolitis obliterans? The worldwide media has jumped at the chance to sensationalise “Popcorn Lung” in the vaping industry, but it seems that very few people have an understanding of what bronchiolitis obliterans is. According to the National Institute of Health’s website on rare and genetic diseases, bronchiolitis obliterans is an inflammatory condition that affects the lung’s tiniest airways. In some cases, those airways will become damaged and inflamed, which can lead to scarring which could block those airways. Although the FDA approved the use of Diacetyl in food flavourings, in 2007, many popcorn companies announced their decision to move away from using flavourings that contain Diacetyl. Some companies are moving towards using real butter, and others are likely to be using acetoin and/or acetyl propionyl.
So it is fair to say that inhaling diacetyl in large and constant quantities like the workers in the popcorn factories can be bad for your health, but how dangerous is it in vapes?
When we look at the potential dangers of diacetyl in e-liquid, it is important to look at the corresponding amount of diacetyl in cigarettes. The diacetyl content in a single cigarette has been averaged at 335.9 micrograms by a study conducted by Fujioka (et al). Assuming that a smoker consumes one pack per day (20 cigarettes), the average daily inhaled dose of diacetyl associated with smoking is therefore 6718 micrograms. While the diacetyl content in e-cigarette cartridges was averaged at 9 micrograms (assuming you go through one cartridge per day), we are looking at a comparison of 6718 micrograms of diacetyl a day for cigarette smokers, and 9 micrograms a day for your average vaper.
This comparison fits perfectly with the most commonly quoted study published by Public England Health, that vaping is 95% less harmful than smoking cigarettes. Although there is a need to look into the long-term effects of vaping, many other studies are further elucidating this under-studied subject. For example, we can look to “Health impact of E-cigarettes: a prospective 3.5-year study of regular daily users who have never smoked” where Riccardo Polosa (et al.) reported on the health outcomes (blood pressure, heart rate, body weight, lung function, respiratory symptoms, exhaled breath nitric oxide, exhaled carbon monoxide, and high-resolution computed tomography of the lungs) of nine daily e-cigarette users who had never smoked, and summarised that, “Even the heaviest [e-cigarette] users failed to exhibit any evidence of emerging lung injury as reflected in these physiologic, clinical or inflammatory measures. Moreover, no changes were noted in blood pressure or heart rate.”
Many e-liquid companies will not add Diacetyl to their e-liquids, preferring, like some popcorn manufacturers, to use acetoin or acetyl propionyl to mimic that buttery flavour we all know and love. The other side of the coin is that acetyl propionyl and acetoin can potentially contain or form trace amounts of Diacetyl under certain conditions, such as the freebase nicotine steeping process. If Diacetyl containing e-liquid contains up to 700 times less Diacetyl than your average cigarette, and acetoin or acetyl propionyl can only attribute to trace amounts, it is still safe to say that vaping is, once again, still a better alternative to smoking.
It is fair to say that the fear-mongering provided by media outlets has contributed to a number of smokers never attempting to vape due to the stigma around vaping and “Popcorn Lung”, although it has been proven time and time again that e-cig use is a better alternative to smoking cigarettes. Tobacco kills nearly 6 million people each year, of whom more than 5 million are from direct tobacco use and more than 600 000 are non-smokers exposed to second-hand smoke. While smoking statistics in New Zealand are steadily dropping (from 25% of adults smoking in 1996, to 16% currently smoking), we still have a long way to go.