The United States National Institute for Occupational Safety and Health has suggested diacetyl, when used in artificial butter flavoring (as used in many consumer foods), may be hazardous when heated and inhaled over a long period.
Workers in several factories that manufacture artificial butter flavoring have been diagnosed with bronchiolitis obliterans, a rare and serious disease of the lungs. The cases found have been mainly in young, healthy, nonsmoking males. As with other end-stage lung diseases, transplantation is currently the most viable treatment option. However, lung transplant rejection is very common and happens to be another setting in which bronchiolitis obliterans is known to occur.
The disease has been called “popcorn worker’s lung” because it was first seen in former workers of a microwave popcorn factory in Missouri, but NIOSH refers to it by the more general term “flavorings-related lung disease”. It has also been called “flavorings-related bronchiolitis obliterans” or diacetyl-induced bronchiolitis obliterans.People who work with flavorings that include diacetyl are at risk for flavorings-related lung disease, including those who work in popcorn factories, restaurants, other snack food factories, bakeries, candy factories, margarine and cooking spread factories, and coffee processing facilities.
In 2006, the International Brotherhood of Teamsters and the United Food and Commercial Workers petitioned the U.S. OSHA to promulgate an emergency temporary standard to protect workers from the deleterious health effects of inhaling diacetyl vapors. The petition was followed by a letter of support signed by more than 30 prominent scientists.The matter is under consideration. On 21 January 2009, OSHA issued an advance notice of proposed rulemaking for regulating exposure to diacetyl. The notice requests respondents to provide input regarding adverse health effects, methods to evaluate and monitor exposure, the training of workers. That notice also solicited input regarding exposure and health effects of acetoin, acetaldehyde, acetic acid and furfural.
Two bills in the California Legislature seek to ban the use of diacetyl.
A 2010 U.S. OSHA Safety and Health Information Bulletin and companion Worker Alert recommend employers use safety measures to avoid exposing employees to the potentially deadly effects of butter flavorings and other flavoring substances containing diacetyl or its substitutes.
A preliminary in vitro study, published in 2012, suggests that diacetyl may exacerbate the effects of beta-amyloid aggregation, a process linked to Alzheimer’s disease. Research in rats and mice has shown that diacetyl can damage the airway and damage cells that line the airway.
In 2015 there were allegations that the health of workers who roast coffee is threatened by diacetyl.