Purpose of review: In 2000, inhalation of butter flavoring vapors was first associated with clinical bronchiolitis obliterans among workers in microwave popcorn production. Toxicologic and epidemiologic studies in the succeeding 5 years have intervention and research implications.
Recent findings: Irreversible obstructive disease exists in workers throughout the microwave popcorn industry, in flavoring manufacture, and in the chemical synthesis of diacetyl, a predominant chemical in butter flavoring. Biologic plausibility of the role of diacetyl and other components of butter flavoring in causing bronchiolitis obliterans exists in rodent experiments which demonstrate respiratory epithelial necrosis. Some risky jobs were associated with short-term peak flavoring exposures, and average 8-h diacetyl exposures as low as 0.02 parts per million were measured in a work area where disease occurred in workers mixing butter flavorings with heated oil.
Summary: Until safe levels of flavoring chemicals are determined, prevention requires substitution, engineering controls, improved work practices, and personal protective equipment to lower exposure, in conjunction with medical surveillance for accelerated declines in pulmonary function. An epidemiologic approach to longitudinal medical surveillance and flavoring chemical exposures, paired with inhalation toxicology studies of flavoring components, will lay the basis for determining health-protective exposure limits for various flavoring chemicals.