Popcorn lung, formally known as bronchiolitis obliterans, is a disease that causes an irreversible narrowing of lung airways. This rare condition initially gained media attention in the early 2000s due to a cluster of cases among microwave popcorn plant workers. In recent years, news media have frequently purported a link between the disease and vaping nicotine. But is there really a connection between popcorn lung and vaping?
Here’s what you need to know to separate fact from fiction about popcorn lung, its potential causes, and whether there is a link between the disease and e-cigarette use.
What is popcorn lung?
Bronchiolitis obliterans, or popcorn lung, is a rare disease in which the bronchioles—the lungs’ smallest airways—become inflamed and ultimately obstructed by scar tissue, making breathing difficult. The damage is irreversible, and while treatments are available, the prognosis for patients is generally poor.
What causes popcorn lung?
The disease is associated with a number of medical and environmental factors. Around half of all lung transplant patients will develop bronchiolitis obliterans syndrome to some degree within five years. Another major risk factor for the condition is exposure to toxic inhalable chemicals used in various industries and professions.
The condition’s link to microwave popcorn gave it its nickname. In the early 2000s, eight cases of bronchiolitis obliterans were reported to Missouri health authorities, with all sufferers reporting former employment at the same microwave popcorn plant. After analyzing the plant and current workers, researchers found the greatest risk for the disease among those employees working with or around the heated oil vats where flavoring agents are added during production. Researchers identified the flavor additive diacetyl—the most prominent chemical in the butter flavor mixture—as the likely cause of workers’ poor lung health.
What is diacetyl?
Diacetyl is a naturally occurring chemical in cultured dairy and fermented products. Both natural and artificial diacetyl are used as flavor additives, giving a variety of packaged foods their butter flavor and aromas, including some flavored coffee beans, margarine, baking sprays, snack foods, and candies, among other items.
Though deemed safe to ingest, animal testing conducted during the last two decades has shown that inhaling diacetyl can be hazardous to lung health. This is because, in its gaseous form, diacetyl irritates the airways. Over time and at a high enough level of exposure, this can trigger lung inflammation, damage, a build-up of scar tissue, and impaired lung function.
Do nicotine e-cigarettes contain diacetyl?
In the early generations of nicotine vapor technology, some brands and flavors of e-cigarettes were found to contain diacetyl, particularly those intended to have a buttery or creamy flavor and aroma. The potential hazard was first identified in a 2014 study that found diacetyl in nearly 70 percent of the 160 e-cigarette products tested. This was quickly followed by a 2015 paper in which researchers at the Harvard T.H. Chan School of Public Health reported finding diacetyl in 39 of the 51 e-cigarette flavors they tested. Due to the known link between inhaled diacetyl and bronchiolitis obliterans, these revelations sparked immediate and widespread concern among health authorities, vapor consumers, and the vapor industry.
In response, the industry across much of the world voluntarily removed diacetyl as a flavoring agent, with some of the largest retailers quickly marketing “diketone-free” e-liquid to consumers now wary of exposure to diacetyl. Governments also took action, with several, such as the United Kingdom, Australia, and the European Union, prohibiting diacetyl in vapor products.
These steps have led to a significant decline in diacetyl-containing e-cigarette products. In a 2021 study, Canadian researchers tested 825 e-cigarettes and found just two products containing diacetyl and zero among the samples collected after 2018.
Do e-cigarettes cause popcorn lung?
The persistence of the idea that vaping is directly linked to popcorn lung has prompted several health bodies, including Health Canada, the New Zealand Ministry of Health, and the UK Health Security Agency, to clarify that no evidence exists for such a link. Independent charities and research institutions, like Cancer Research UK and Action on Smoking and Health, have made similar statements. Yet, the myth continues to appear in news headlines around the world. (Credit where credit is due: The Washington Post, at least, published an article in 2019 debunking the myth.)
These misleading headlines are being published at the same time anti-tobacco organizations are continuing to promote the mythical link between vaping and popcorn lung as a reason to support more restrictive policies on e-cigarettes. But, contrary to what frightening headlines would have you believe, there is no evidence that e-cigarettes cause popcorn lung. In fact, all of the evidence points to the contrary.
For one thing, with the rise in popularity of e-cigarette use over the last 15 years, one would expect a concurrent increase in popcorn lung cases where the two are related. The news media periodically reports on individuals suffering from alleged vaping-induced popcorn lung, but none have been confirmed. Health authorities report no increase in bronchiolitis obliterans. Some countries’ health departments, such as Canada’s, have even admitted that there has never been a confirmed case of e-cigarette-associated popcorn lung in their country’s history.
More importantly, if vaping nicotine e-cigarettes increases the risk of popcorn lung, one should expect an even clearer connection between popcorn lung and traditional smoking. Conventional combustible cigarettes contain diacetyl—significantly more than what was found in even early-generation e-cigarettes before voluntary industry changes and governmental prohibitions on diacetyl in e-cigarettes.
The 2015 Harvard study, for example, found an average of nine micrograms of diacetyl per e-cigarette cartridge in the samples that tested positive for the chemical. Combustible cigarettes, meanwhile, contain approximately 336 micrograms of diacetyl per cigarette. This means that a cartridge-per-day vaper would be exposed to just nine micrograms of diacetyl, while pack-per-day smokers are exposed to more than 6,700 micrograms of diacetyl every day—750 times more diacetyl exposure than vapers. Yet, a link between smoking and popcorn lung has yet to materialize. In fact, during the initial studies of popcorn factory workers, researchers observed that those employees who reported smoking showed fewer signs of bronchiolitis obliterans than their non-smoking counterparts.
If smokers are at no greater risk of popcorn lung because of the diacetyl in cigarettes, why would nicotine vapers be at risk of the disease when their exposure to diacetyl is several hundred times less than smokers? The answer: They aren’t.
The myth that vaping causes popcorn lung continues to haunt the discourse around e-cigarettes in part because it is a sensational idea. Tragic stories of individuals allegedly stricken ill by a controversial product, like e-cigarettes, make for attention-grabbing news headlines and fodder for anti-tobacco advocates. But, the glaring lack of concrete evidence refutes the notion that vaping causes popcorn lung. E-cigarettes may not be free of risk, but the facts are that they are significantly safer than smoking, and whatever risks might be associated with vaping, popcorn lung is not one of them.