Diacetyl is a byproduct of fermentation.  It is composed of carbon, hydrogen and oxygen atoms and has the molecular formula C₄H₆O₂.  Diacetyl occurs naturally in alcoholic beverages and is added to some foods to impart a buttery flavor.

In recent years, diacetyl has been implicated as the cause of the newest occupational lung disease: flavorings-induced bronchiolitis obliterans.  Bronchiolitis obliterans is a very rare lung disease that typically occurs as a complication of organ transplantation, is progressive and is generally considered to be incurable, other than by lung transplantation.  Bronchiolitis obliterans is a “fixed” obstructive lung disease, meaning that pulmonary function does not appreciably improve with bronchodilation.  In the early stages of flavorings-induced bronchiolitis obliterans, obstruction is not fixed and the disease is often diagnosed as asthma.

Bronchiolitis obliterans has been diagnosed among production workers in diacetyl manufacturing plants, among exposed workers in flavoring plants (especially those who mix flavorings or heat diacetyl), among exposed workers in microwave popcorn manufacturing plants, and among a few consumers who consumed large quantities of microwave popcorn and who liked the smell of popcorn and regularly inhaled its vapors, unaware of the lung hazards.

The Metzger Law Group began litigating cases of flavorings workers in 2007 when physicians affiliated with UCLA and USC began diagnosing this rare disease in exposed flavorings workers and referred the sick workers to the firm for legal representation.  Currently, the firm is representing workers who developed bronchiolitis obliterans from exposure to diacetyl at Carmi Flavors & Fragrance Company and Gold Coast Ingredients, both located in the City of Commerce.  Several of these workers are totally disabled from bronchiolitis obliterans.  Some have received lung transplants and others are awaiting lung transplantation.