It should come as no surprise to most consumers that many of the flavors found in modern packaged food products are created through the use of chemical flavorings. One example of such is diacetyl, a chemical used in artificial butter flavoring which is commonly found in microwave popcorn. Studies have linked diacetyl with the development of the lung disease bronchiolitis obliterans (a widespread inflammatory and fibrotic obstruction of the small airways) in industrial flavor workers who experience significant inhalation exposure to the chemical, and various health advocates have pointed to those studies as a reason to call for more stringent governmental regulation over (or an outright ban on) the use of diacetyl.
The question on many people's minds, then, is if the link between diacetyl inhalation and bronchiolitis obliterans (also known as BO, or "popcorn lung") in industrial workers is indeed causal, does diacetyl pose a danger to consumers with much lower levels of exposure to diacetyl than factory workers, consumers who merely breathe in fumes produced during the heating of artificially butter-flavored microwave popcorn products? This issue gained prominent public attention in September 2007 via the publication of a letter sent to federal agencies by Dr. Cecile Rose, a pulmonary specialist at Denver's National Jewish Medical and Research Center, saying that doctors at the center believed they had encountered the first case of a consumer's developing lung disease from the fumes of microwave popcorn.
Whether this disclosure demonstrates that microwave popcorn poses a significant health risk to ordinary consumers is not so cut-and-dried, though. As Dr. Rose noted, "This is not a definitive causal link" and "We cannot be sure that this patient's exposure to butter flavored microwave popcorn from daily heavy preparation has caused his lung disease" (although she also noted that doctors had "no other plausible explanation" for the patient's symptoms and that the issue "raises a lot of questions and supports the recommendation that more work needs to be done"). Additionally, this case might represent far more of an extreme than a norm, as the patient involved "did report daily consumption of several bags of extra butter flavored microwave popcorn for several years" (at least two bags per day for more than 10 years) and "when he broke open the bags, after the steam came out, he would often inhale the fragrance because he liked it so much."
Shortly after the publication of Dr. Rose's letter, the producers of four of the biggest-selling microwave popcorn brands in the U.S. (Orville Redenbacher, Act II, Pop Secret, and Jolly Time) announced that they were working to remove diacetyl from their microwave popcorn recipes (while nonetheless reassuring consumers about the safety of their products).