Identification

• In bronchiolitis obliterans, the smallest lung airways (bronchioles) become progressively more scarred and narrowed, causing breathing problems.
  
  

Symptoms

• The main symptoms include dry cough, wheezing, and worsening shortness of breath during exertion, according to the U.S. National Institute for Occupational Safety and Health (NIOSH). Symptoms usually develop gradually, but can occur suddenly in some people.
  
  

Significance

• The workers may experience a slow improvement of lung function once they are no longer exposed to flavoring vapors, but usually some degree of lung dysfunction continues, NIOSH cautions. Severe cases require lung transplants.
  
  

Diacetyl

• A study published in a 2008 issue of Toxicologic Pathology found that a chemical used in microwave popcorn flavoring, diacetyl, damaged the respiratory tracts of rats. Manufacturers of popcorn brands Orville Redenbacher, Jolly Time and others discontinued use of diacetyl.
  
  

Consumers

• The condition is not linked to consumer use, but one individual has sued the stores where he bought microwave popcorn after being diagnosed with bronchiolitis obliterans, as reported by the Associated Press in January 2008. He stated he previously ate two bags of microwave popcorn a day.