Will Diacetyl Flavorings in E-Cigarettes be the Next Mass Tort?

Posted by on January 29, 2016

This post also appears on Goldberg Segalla’s Product Liability Playbook Blog. This post was co-authored by Giovanni Ciavarra, Ph.D. of Innovative Science Solutions, and Christopher P. Midura of Goldberg Segalla.


It seems that science related to the efficacy and safety of e-cigarettes (e-cigs) is continuously making headlines.

The growing popularity of e-cigs has attracted attention of many different groups, and e-cigs are likely to continue to be the subject of vigorous debate. While e-cigs are not currently regulated, the FDA has issued a proposed rule to include e-cigs under its authority to regulate certain tobacco and nicotine-containing products. Previously, we have covered some of these issues in other posts and readers are directed to some of these posts here, here, and here.

With regard to safety of e-cigs, most of the research has focused on nicotine exposure, and exposure to e-cig aerosols and vapors (first and second-hand exposure) which can contain nanoparticles, heavy metals, formaldehyde and other constituents. Another safety issue is related to the actual devices themselves. Instances of exploding e-cig devices have triggered numerous lawsuits.

Recently, scientists at the Harvard T.H. Chan School of Public Health published a study reporting that diacetyl — a flavoring agent — was detected in more than 75 percent of flavored e-cig liquids (i.e. the nicotine-containing liquid that is heated and vaporized). While other studies previously also detected diacetyl in e-cig liquids, this new study is potentially significant since the diacetyl was detected in the vapor, thus providing potential evidence for a diacetyl exposure pathway via the respiratory tract.

In this context, as most of our readers know, diacetyl has been on the radar screen of government regulators and litigators for many years for its purported role in various pulmonary injuries (see our DRI paper titled: Lung Disease from Microwave Popcorn Flavoring? Searching for Kernels of Truth in the Litigation ‘Maize). Diacetyl is a natural byproduct of fermentation, and is found at low concentrations in a wide variety of foods including beer, wine, fruits, and butter. Diacetyl is also produced chemically as a volatile ketone and has been used as a flavoring agent in food manufacturing for nearly 50 years. It imparts certain flavor characteristics to foods, such as providing the “buttery flavor” in microwave popcorn. A number of years ago, the use of flavorings (such as diacetyl) in food products came to a head after reports of various pulmonary diseases in seemingly healthy microwave popcorn workers. In these cases, workers alleged that they were not warned of the dangers in using butter flavor compounds in the production of microwave popcorn and other food products.

At the time these initial occupational lawsuits were initiated, little attention was given to the potential effects of diacetyl on consumers. Eventually, however, the plaintiffs’ bar increased its efforts to established a conclusive link between diacetyl exposure to consumers and pulmonary injuries. While some consumer-based diacetyl litigation was initiated related to microwave popcorn consumption, diacetyl did not become the next asbestos in the mass tort world.  In fact, in the most recent consumer based “popcorn lung” case to be tried, Stults v. International Flavors and Fragrances, Inc., et als., an Iowa Federal Court jury returned a defense verdict. The Stults case illustrates a common theme in both occupational and consumer-based diacetyl litigation. That is, the reliability and admissibility of expert testimony bearing on the causal link between diacetyl exposure and pulmonary injuries. Often, as was the case in Stults, the defense is successful in either 1) admitting expert testimony suggesting that the plaintiff’s alleged pulmonary injuries were not caused by diacetyl exposure, or 2) excluding, as speculative or unreliable, expert testimony purporting to clearly establish the causal link in a respective case.

The diacetyl landscape, and resulting litigation, continues to evolve. Intense scientific and regulatory scrutiny of diacetyl has occurred in the context of its alleged role in various pulmonary injuries, including asthma, bronchiectasis, bronchiolitis obliterans, chronic bronchiolitis, chronic obstructive pulmonary disease, emphysema, and severe lung impairment. While some individuals in the medical, scientific, government, and regulatory communities have suggested a causal link between respiratory exposure to diacetyl and other flavorings and pulmonary injury, it still remains unclear whether exposure to diacetyl alone is capable of causing disease, or whether it is diacetyl along with mixtures of volatile organic compounds that result in disease.

In the new Harvard study, the investigators fully discharged the contents of the e-cigs and the air stream was captured and analyzed for the three flavoring chemicals. The authors reported that at least one flavoring chemical was detected in 92 percent(47 of 51) of unique flavors tested. With regard to diacetyl, it was detected above the laboratory limit of detection in 76 percent (39 of the 51) flavors tested.

While this study has generated fodder for opponents of e-cigs, it is important to keep the findings in context. Below we provide a few points for consideration:

  • No Biological Effects Measured: Researchers did not measure any biological effects, including no endpoints related to pulmonary disease.


  • Exposure Levels: Based on the levels of diacetyl in this study, the potential for adverse human health effects is likely minimal, and needs to be put into the proper context. For example, cigarette smoke is known to produce much higher levels of diacetyl than e-cig vapor, and yet, cigarette smoke has not been shown to be a risk factor for bronchiolitis obliterans, the specific pulmonary condition that is often cited to be linked to diacetyl exposure.


  • Not Generalizable to all E-Cigs: As noted by the authors: “the extent to which are [sic] results are generalizable to the entire population of e-cigarette flavors is simply unknown.” Since flavoured e-cig liquids are the ones most likely to contain these flavoring chemicals, the overall prevalence of these constituents in e-liquids is likely much lower.

The question of whether diacetyl in e-cigs will form the basis for the next mass tort remains to be seen. Given the growing popularity of e-cigs, and the continued media attention on their use, it is not difficult to envision increased litigation in this field. However, notwithstanding the existence of the new Harvard study, the arguments that have led to defense verdicts in previous pieces of diacetyl litigation remain viable. Manufacturers, suppliers, and retailers of e-cigs and diacetyl are encouraged to stay abreast of this issue as it develops.

Giovanni Ciavarra, Ph.D.

Christopher P. Midura, Esq.

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