Popcorn lung, or bronchiolitis obliterans, is a rare condition involving scarring of the small airways, sometimes linked to inhaling certain chemical fumes. With the rise of vaping, questions have grown about whether e-cigarettes can cause this condition, especially early reports pointing to diacetyl as a possible culprit. This article explains what popcorn lung is, how diacetyl and related flavoring chemicals factor into risk, what peer-reviewed studies and health agencies report about vaping, and how current evidence and public health guidance address concern about vaping and long-term lung injury.
What Is Popcorn Lung (Bronchiolitis Obliterans)?
Bronchiolitis obliterans is a condition in which the small airways in the lungs become inflamed and scarred, narrowing passages and making breathing difficult. The nickname popcorn lung originated from cases in the early 2000s among microwave popcorn factory workers who inhaled high levels of diacetyl vapors during production. While the severe occupational exposures in those workplaces drew attention, the term now refers more broadly to bronchiolitis obliterans regardless of cause, which can result from infections, autoimmune diseases, medications, environmental exposures, and, in rare instances, e-cigarette use.
Diacetyl, Acetoin, and 2,3-Pentanedione in Vaping
Chemicals of Concern
Diacetyl, acetoin, and 2,3-pentanedione are flavoring compounds that, at very high inhaled concentrations, have been shown to cause airway damage in animal and occupational studies. Diacetyl is notorious for its butter-like flavor and was historically used in many custard and sweet-flavored e-cigarette liquids. While diacetyl occurs naturally in some foods like butter and coffee at trace amounts, inhalation exposure in occupational settings has been clearly associated with bronchiolitis obliterans.
E-Cig Aerosol Exposure Is Different
In e-cigarettes, these flavorings are heated into an aerosol that users inhale. The key question is whether the levels reached in vaping aerosol pose meaningful risk. Multiple regulatory and research bodies have found that e-cigarette users can be exposed to diacetyl and related compounds, typically at lower levels than seen in heavily exposed occupational settings, but potentially at levels higher than in non-vaping air.
| Exposure Source | Diacetyl Level (approximate, when reported) | Context |
|---|---|---|
| Microwave popcorn production (occupational) | Very high, documented in cases of bronchiolitis obliterans | Sealed vapor in poorly ventilated spaces |
| Traditional combustible cigarette smoke | Low to moderate, depending on brand | Chronic smoke exposure |
| E-cigarette aerosol (varies by product and flavor) | Detectable; some flavored pods and tanks show higher levels | Varies by device, flavorings, and coil type |
| Ambient air (non-vaping, non-smoking) | Very low or not detectable | Background environmental air |
What Regulators and Health Agencies Say
Agencies such as the U.S. Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), and the European Food Safety Authority (EFSA) have reviewed the evidence on diacetyl in e-cigarettes. Their findings generally indicate that, while certain flavored e-cigarettes can contain diacetyl and other potentially harmful flavor compounds, current data do not establish that vaping causes popcorn lung at population levels. However, agencies emphasize avoiding unnecessary inhalation exposures and call for continued research and product regulation.
What the Evidence Shows About Vaping and Lung Disease
EVALI and Known Harms
The most well-defined lung injury linked to vaping in the U.S. was E-cigarette or Vaping Product Use-Associated Lung Injury (EVALI), which emerged in 2019 and was strongly associated with vitamin E acetate in illicit THC-containing products. EVALI presented differently from classic bronchiolitis obliterans, with distinct imaging and clinical features. By late 2020, EVALi cases declined sharply after public health guidance removed vitamin E acetate from illicit products. While EVALI raised awareness of vaping-related lung injury, it is not synonymous with popcorn lung.
Bronchiolitis Obliterans Reports
There have been rare case reports in medical literature describing patients with bronchiolitis obliterans who had a history of e-cigarette use. These individual cases are important for clinical awareness, but they do not establish causation at the population level, nor do they indicate how common such outcomes may be. Most e-cigarette users do not develop these injuries, though they may still experience other respiratory effects like coughing or wheezing, particularly among people who were previously smoking.
Current Consensus and Practical Takeaways
The current scientific consensus is that while e-cigarette aerosol is not harmless and can contain potentially harmful chemicals such as diacetyl, there is no conclusive evidence that vaping causes popcorn lung in humans under real-world conditions. Popcorn lung remains exceptionally rare and has been primarily documented in occupational inhalation settings with very high exposures. Compared with combustible cigarettes, e-cigarettes are likely less harmful for adult smokers who switch completely, though they are not risk-free. The strongest protective action users can take is to avoid unnecessary inhalation of flavoring chemicals, rely on regulated products where available, and stay updated on public health advisories.
Key Comparisons at a Glance
| Comparison Dimension | Popcorn Lung from Occupational Exposure | E-Cigarette Use (Current Evidence) | Combustible Cigarette Smoking |
|---|---|---|---|
| Primary Exposure Source | High-concentration diacetyl vapors in food production | Variable levels of diacetyl and other flavorings in aerosol | Complex mixture of thousands of chemicals, including some flavor compounds |
| Typical Lung Injury Pattern | Bronchiolitis obliterans (scarring of small airways) | EVALI with distinct features; rare bronchiolitis obliterans cases reported | Chronic obstructive pulmonary disease (COPD), emphysema, increased infection risk |
| Documented Cases | Documented clusters among workers with high-level occupational exposure | Few case reports; not established as a common outcome | Millions of cases of smoking-related lung disease globally |
| Regulatory Status | Recognized occupational hazard; strict exposure limits | Subject to regulation in many regions; some flavorings restricted | Heavily regulated with health warnings |
Reducing Risk and Making Informed Choices
Adult smokers considering vaping as a less harmful alternative should seek regulated products and avoid modified devices or non-regulated markets. People who vape can reduce potential exposure to diacetyl and other flavoring chemicals by choosing products with transparent ingredient labeling, avoiding flavors described as buttery, creamy, or strongly sweet when possible, and not adding substances to e-cigarette devices that are not designed for them. Policies that limit certain flavorings in tobacco and nicotine products can reduce population-level exposure, while continued research will clarify long-term risks.
Bottom Line
Popcorn lung is a serious but very rare lung condition historically linked to high-level occupational exposure to diacetyl. Although some e-cigarette products contain diacetyl and other potentially harmful flavoring chemicals, current evidence does not show that vaping causes popcorn lung at the level seen with occupational exposures. E-cigarettes are not risk-free and are best used by adult smokers as a complete replacement for combustible cigarettes, not by non-smokers. Staying informed, using regulated products, and minimizing unnecessary inhalation exposures are the most practical steps for reducing risk.