Many lawsuits have been filed by employees of flavoring companies that used diacetyl as an ingredient, claiming long-term exposure to the substance has caused a nonreversible respiratory disease called bronchiolitis obliterans.
Bronchiolitis obliterans is a serious lung disease in which the smallest airways of the lungs become scarred and restricted, diminishing breathing. It is often misdiagnosed as asthma, bronchitis, emphysema or even pneumonia because the symptoms are similar, with a patient coughing, wheezing, experiencing shortness of breath and fatigue. The only treatment for bronchiolitis obliterans is a lung transplant.
Diacetyl has been found in many products such as microwave popcorn, flavored coffee, baking products, beer and e-cigarette liquid. It has largely been phased out of modern foods, but is still prevalent in vaping juice. It is used to mimic the smooth, creamy flavor of butter.
A different chemical known as acetyl propionyl (AP), or 2,3-pentanedione, has been used in place of diacetyl. Even though it has been approved for use in food consumption, there have been many concerns raised about the inhalation of AP. In lab tests, it has been found to have the same effect on the lungs of rodents as diacetyl does on human lungs. The Center for Disease Control and Prevention (CDC) is concerned with the possibility that AP seems to share the same mechanism of toxicity as diacetyl.
The Flavor and Extract Manufacturers Association (FEMA) has identified 27 flavoring agents that they consider to be a “high priority” threat to respiratory health. Both diacetyl and AP are listed as “high priority” by FEMA.