Diacetyl (2,3-butanedione), a naturally occurring, organic flavoring compound commonly used to produce the flavor and aroma of buttery and creamy notes in various foods and e-liquids, is considered safe to ingest however has been shown to be linked to serious lung disease when inhaled. As such, diacetyl has become a controversial topic of debate and regulatory concern in the vaping industry.
The Nature of Diacetyl: A Flavoring with a Cloudy History
Diacetyl is an organic compound that is naturally created through fermentation and synthesized for use as a flavoring agent. It has a distinctive buttery flavor and is a common ingredient in dairy products, candies and baked goods. In the vaping industry, diacetyl is widely used to enhance the flavor and aroma of desserts, custards and creamy e-liquids. Many informed vapers have had a strong reason to suspect that e-liquids labeled as "pastry", "custard" or "cream" contained either diacetyl or one of its synthetic relatives, and therefore sought clarification from manufacturers about the presence of these ingredients in their products.
The Origin of "Popcorn Lung": A Workplace Hazard
While the vaping community has been alarmed by the possibility of developing "popcorn lung" when vaping diacetyl-containing e-liquids, it is important to note that the serious health problems caused by the inhalation of diacetyl actually originated from the food industry. Workers at a microwave popcorn factory developed bronchiolitis obliterans, a permanent and debilitating lung disease characterized by scarring of the bronchioles and obstruction of airflow, after years of exposure to diacetyl vapor in a factory setting. The NIOSH investigated the cause of the disease and determined that the high concentrations of diacetyl vapors in the factory contributed to the development of the lung disease.
Why Was Diacetyl Used in Microwave Popcorn?
As mentioned above, the same type of buttery flavoring used to make microwave popcorn is commonly found in many e-liquids. Researchers identified the link between diacetyl and vaping in 2015, when researchers tested samples of 51 different flavored e-cigarettes and found diacetyl in 39 (76%) of the samples. The fact that the vaping population was exposed to diacetyl through the inhalation route, similar to how the microwave popcorn workers were exposed to diacetyl through the inhalation route, sparked widespread fear in the vaping community.
Vape Aerosol vs. Cigarette Smoke
A key part of the diacetyl debate is the comparison of risk between vaping aerosol and cigarette smoke. Data shows that while there is diacetyl in some e-liquids, the concentration is much less than what is found in cigarette smoke. An analysis of diacetyl levels in tobacco smoke and e-liquids, provided by a reputable vape retailer, shows that tobacco smoke contains 335.9 micrograms of diacetyl, whereas e-liquids contain 9.0 micrograms of diacetyl. The Centers for Disease Control and Prevention (CDC) states that e-cigarette aerosol typically contains fewer harmful chemicals than the 7,000+ chemicals found in tobacco smoke. Therefore, smokers switching to vaping will likely decrease their exposure to diacetyl significantly, although the safest option is still to inhale neither.
Diketones: More Than Just Diacetyl
The controversy surrounding diacetyl in vaping goes beyond diacetyl itself and into the broader family of chemicals known as diketones. Two of diacetyl’s close relatives – acetoin and 2,3-pentanedione – were found in 46 and 23 of the 51 samples tested in the aforementioned 2015 study, respectively. Both of these diketones are commonly used as replacements for diacetyl in e-liquids, and 2,3-pentanedione has a similar chemical structure to diacetyl and research indicates it may pose similar inhalation risks. Therefore, if you are looking to avoid all diketones, simply buying e-liquids with “diacetyl-free” labeling is not enough; you need to purchase from a brand that explicitly tests for and guarantees the absence of all diketones.
The Global Regulatory Response to Diacetyl in Vaping Products
The global regulatory response to diacetyl in vaping products is inconsistent and affects the safety of the market. The U.K. has outright banned the use of diacetyl in e-liquids. Therefore, any legally sold e-liquids in the U.K., including those by Pod Salt, cannot contain diacetyl. However, in the U.S., the FDA has been criticized by the American Lung Association for delaying the review of vaping product ingredients, allowing e-liquids with diacetyl to remain on the market until recently. The inconsistency in regulations across jurisdictions creates a complex environment for consumers to navigate and greatly increases the likelihood of risk exposure.
Identifying and Choosing Diacetyl-Free E-Liquids
Identifying true diacetyl-free products requires diligence, as diacetyl can be an unknown ingredient in flavor concentrate blends. Reputable brands in the industry now commit to independent third-party laboratory testing of their products (e.g., Enthalpy Labs) and disclose the results publicly. I have observed that reputable manufacturers are usually transparent about their policies regarding diacetyl-free products. For example, Freeman Vape Juice discloses that its "Cocaine" flavor contains a minimal amount of diacetyl to create a buttery cookie flavor profile, while its other product lines are diketone-free. Some well-known brands that have made commitments to be diacetyl-free include Black Note (tobacco-based flavors) and VaporFi.
The Manufacturer’s Predicament: Honesty, Ignorance, and Labeling
It is essential to recognize that not all instances of diacetyl in e-liquids resulted from manufacturers intentionally adding the chemical. At the inception of the vaping industry, many small manufacturers of e-liquids prepared their own e-liquids using commercially available food-grade flavorings, without knowing the complete composition of the chemicals involved in the flavorings. Because diacetyl was occasionally present in commercial flavorings in trace amounts, even when a manufacturer did not intentionally add diacetyl to their product, it could be present in the final product. Therefore, the safest way to purchase diacetyl-free products is to buy from a large and established manufacturer that employs chemists and maintains strict control over the sourcing of all ingredients, as opposed to purchasing from small, untested manufacturers.
What Hasn’t Been Resolved Yet: Is There Ever Safe Exposure?
Although major health organizations clearly state that diacetyl is “safe to eat but not to inhale” due to the way the lungs metabolize substances differently than the stomach, the scientific and public health communities are still debating whether any inhalation of diacetyl poses a risk. While the exposure to diacetyl from vaping is several orders of magnitude lower than the workplace exposures that led to the diagnosis of "popcorn lung" in the microwave popcorn workers, the CDC, American Lung Association, and American Cancer Society all classify diacetyl as a hazardous substance in e-cigarette aerosol. Proponents of vaping as a method of reducing harm cite the lack of reported cases of "popcorn lung" in vapers, but toxicologists continue to warn of the dangers of the irreversible lung damage caused by the inhalation of diacetyl.
Your Individual Risk Assessment: Making Choices as a Vaper
Ultimately, your decision to vape or not vape is dependent upon individual risk assessment. For someone who currently smokes, switching to vaping is likely to result in a safer overall choice, even if the e-liquids do contain some diacetyl. If you are a non-smoker or can choose to vape, choosing diacetyl-free e-liquids that have been tested independently and have no detectable levels of diacetyl will eliminate a known, preventable risk. In my opinion, the availability of numerous high-quality, flavorful diacetyl-free products from reputable manufacturers such as Kind Juice makes this a simple choice. The responsibility rests with both the consumer to demand transparency and the manufacturers to provide it.