It’s called popcorn lung because the condition was first identified in workers at a microwave popcorn factory. In the early 2000s, employees at a Missouri facility developed a rare, severe lung disease after breathing in artificial butter-flavoring chemicals day after day. The culprit was diacetyl, a compound that gives microwave popcorn its buttery taste and smell. The nickname stuck, and it’s been used ever since to describe the medical condition known as bronchiolitis obliterans.
The Missouri Factory That Started It All
Between 2000 and 2002, the CDC documented cases of fixed obstructive lung disease among workers at a microwave popcorn factory in Missouri. These workers had been handling pure diacetyl and breathing in its vapors during production. Animal studies confirmed that inhaling diacetyl causes severe damage to the lining of the airways. As investigations expanded, the same disease turned up in popcorn factory workers across Missouri, Iowa, Ohio, New Jersey, and Illinois.
The pattern was clear: people who worked around large quantities of heated diacetyl were developing a rare lung condition at alarming rates. Because the connection to the popcorn industry was so direct and so dramatic, the media and medical community began calling it “popcorn lung,” a name far easier to remember than bronchiolitis obliterans.
What Actually Happens Inside the Lungs
Popcorn lung involves inflammation and scarring of the tiny airways deep in the lungs, called bronchioles. Over time, that scarring thickens and narrows these passages, trapping air inside and making it harder to breathe out. The damage is chronic and irreversible. Unlike asthma, where airway narrowing comes and goes, the obstruction in popcorn lung is fixed. The scarred tissue doesn’t relax or heal.
On a CT scan, doctors look for a combination of two key signs: widened airways (because the walls have been damaged) and trapped air that doesn’t escape when you exhale. That pairing of findings appears almost exclusively in bronchiolitis obliterans and helps distinguish it from other lung conditions.
Symptoms and How They Progress
Popcorn lung often develops gradually, and you may not notice symptoms at first. As the scarring worsens, the most common signs include:
- Shortness of breath, especially during or after physical activity
- A dry, persistent cough that sometimes produces mucus
- Wheezing
- Unusual fatigue
These symptoms overlap with many other respiratory conditions, which is part of why popcorn lung can be difficult to diagnose early. The shortness of breath tends to get worse over time as more scar tissue builds up, and because the damage can’t be reversed, early detection matters.
Diacetyl and Its Replacement Aren’t That Different
Diacetyl is the primary chemical behind the condition, but it’s not the only one that poses a risk. After the popcorn factory cases made headlines, many manufacturers switched to a substitute called acetyl propionyl (2,3-pentanedione). The two chemicals are structurally very similar, differing by just one carbon atom, and workplace safety agencies treat both as hazardous to the lungs.
The safety limits for these chemicals are extremely low. NIOSH recommends that workers breathe no more than 5 parts per billion of diacetyl and 9.3 parts per billion of acetyl propionyl over an eight-hour shift. To put that in perspective, those are some of the strictest exposure limits for any flavoring chemical. Despite these recommendations, OSHA has no enforceable standard for diacetyl or related flavorings, meaning compliance is technically voluntary for employers.
The Vaping Connection
Popcorn lung gained a second wave of attention when researchers found diacetyl in e-cigarette liquids, particularly those with sweet or buttery flavors. A risk assessment published in Science of the Total Environment modeled the daily diacetyl dose that teen and adult vapers inhale and compared it to NIOSH safety benchmarks. Every scenario they tested exceeded the threshold for concern, with hazard values ranging from about 6 to nearly 300 times the safe level.
That said, vaping-related lung injuries that made headlines in 2019 were mostly a different condition called EVALI. The key distinction: EVALI was primarily caused by vitamin E acetate, a thickening agent in black-market cannabis vape cartridges. It damages the air sacs where oxygen exchange happens. Popcorn lung damages the small airways that carry air to those sacs. They’re different diseases in different parts of the lung, caused by different chemicals, though both are linked to inhaled substances.
Treatment Slows It but Can’t Cure It
Because the scarring is permanent, treatment for popcorn lung focuses on slowing progression and managing symptoms. The first step, when the cause is chemical exposure, is removing the source entirely. Beyond that, the most common approaches include anti-inflammatory medications to reduce swelling in the airways and bronchodilators that relax the muscles around the breathing tubes to help keep them as open as possible. For people whose blood oxygen drops too low, supplemental oxygen may be necessary.
In the most severe cases, when the disease progresses despite treatment and becomes life-threatening, a lung transplant may be the only remaining option. This is rare, but it underscores why the condition is taken so seriously, particularly in occupational settings where exposure can be controlled.