Sparked by an unusually high incidence of lung disease in workers at popcorn factories, researchers are investigating ingredients in the buttery snack. Their research is focused on diacetyl, the ingredient largely responsible for the odor and flavor of butter in popcorn.
Diacetyl is easily vaporized at temperature used in microwave popcorn production, resulting in high concentrations in the workplace. This prompted a study by the National Institute for Occupational Safety and Health, which studied the acute toxicity of inhaled diacetyl in rats and compared different exposure patterns. Diacetyl, including just its vapor form, was found to injure lungs.