In 2007, health officials in California revealed that numerous workers in local flavoring factories suffered from a rare, life-threatening lung condition called bronchiolitis obliterans, later nicknamed “popcorn lung.” The illness, which scars the air sacs of the lungs and makes breathing difficult, stemmed from exposure to diacetyl, a yellow chemical used to give microwave popcorn its buttery flavor. Now, that chemical is at the center of a new study revealing that it’s harmful in vape liquids as well.
In the study, published Friday in Scientific Reports, researchers from Harvard’s T.H. Chan School of Public Health show that diacetyl, together with a similar chemical called 2,3-pentanedione, can impair the function of the lungs when it’s inhaled. Flavoring chemicals are found in over 90 percent of commercially marketed flavored e-cigarettes, and of those chemicals, diacetyl, is the most common, the authors report. 2,3-pentanedione is used as a substitute in e-liquids, they add, likely because diacetyl is associated with popcorn lung. The European Union banned diacetyl in vape liquids in 2016.
Though these chemicals are considered safe ingredients to ingest in food, diacetyl’s history strongly suggests that it’s not safe to breathe in, especially not in vape form. Workers in flavoring factories now receive warnings about the dangers of inhaling flavoring chemicals, said co-senior author Joseph Allen, Ph.D., who asked: “Why aren’t e-cig users receiving the same warnings?”
Allen and another co-senior author, Quan Lu, Ph.D., led a team who investigated what these chemicals do to the human lung. Rather than experiment on actual humans, they used normal human bronchial epithelial cells — the ones lining the lung — in a system closely mimicking a living human airway.
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