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This topic page provides a resource for findings and recommendations by the National Institute for Occupational Safety and Health (NIOSH) to reduce the risk of severe obstructive lung disease (obliterative bronchiolitis) associated with occupational exposures to flavorings.



In August 2000, the Missouri Department of Health and Senior Services requested technical assistance from NIOSH in an investigation of bronchiolitis obliterans (also known as obliterative bronchiolitis) in former workers of a microwave popcorn plant in Jasper, Missouri. Obliterative bronchiolitis is a serious lung disease that is irreversible. The Missouri request led to intensive NIOSH research performed in collaboration with the microwave popcorn industry and flavorings manufacturers. The findings from that research provided a basis for a 2004 NIOSH Alert: Preventing Lung Disease in Workers Who Use or Make Flavorings. In addition to the full Alert in English, a Summary Sheet is available in Spanish (en Español) . Although much remains unknown regarding the toxicity of flavoring-related chemicals, employers and workers can take steps to address working conditions and work practices that place workers at risk.

Flavorings-Related Lung Disease

Microwave popcorn plant and flavoring plant workers have developed obstructive lung disease, which can be very severe. In many cases where lung biopsies were done, a type of bronchiolitis called constrictive bronchiolitis obliterans was found. In this disease, the smallest airways in the lung (the bronchioles) become scarred and constricted, blocking the movement of air.


The main respiratory symptoms experienced by workers affected by obliterative bronchiolitis include cough (usually without phlegm), wheezing, and worsening shortness of breath on exertion. The severity of the lung symptoms can range from only a mild cough to severe cough and shortness of breath on exertion. These symptoms typically do not improve when the worker goes home at the end of the workday or on weekends or vacations. Usually these symptoms are gradual in onset and progressive, but severe symptoms can occur suddenly. Some workers may experience fever, night sweats, and weight loss. Before arriving at a final diagnosis, doctors of affected workers initially thought that the symptoms might be due to asthma, chronic bronchitis, emphysema, pneumonia, or smoking.

Medical Tests

Medical testing may reveal several of the following findings:

  • Spirometry, a type of breathing test, often shows fixed airways obstruction (i.e., difficulty blowing air out fast and no improvement with asthma medications) and sometimes shows restriction (i.e., decreased ability to fully expand the lungs). Lung volumes may show hyperinflation (i.e., too much air in the lungs due to air trapping beyond obstructed airways).
  • Diffusing capacity of the lung (DLCO), a type of breathing test, is generally normal, especially early in the disease.
  • Chest X-rays are usually normal but may show hyperinflation.
  • High-resolution computerized tomography (HRCT) scans of the chest at full inspiration and expiration may reveal heterogeneous air trapping on the expiratory view as well as haziness and thickened airway walls.
  • Lung biopsies may reveal evidence of constrictive bronchiolitis obliterans (i.e., severe narrowing or complete obstruction of the small airways). An open lung biopsy, such as by thoracoscopy, is required for a pathologic diagnosis (in contrast to a transbronchial biopsy). Special processing, staining, and review of multiple tissue sections may be necessary for a diagnosis. However, even open lung biopsy appears to be insensitive because of the patchiness of the pathologic abnormality and the ease with which the diagnosis has been initially missed even by experienced chest pathologists.

Medical Management

Workers should be promptly referred for further medical evaluation if they have persistent cough; persistent shortness of breath on exertion; frequent or persistent symptoms of eye, nose, throat, or skin irritation; abnormal lung function on spirometry testing; or accelerated decline in lung function. Physicians should advise workers about any suspected or confirmed medical condition that may be caused or aggravated by work exposures, about recommendations for further evaluation and treatment, and specifically about any recommended restriction of the worker's exposure (including removal from the workplace) or use of personal protective equipment. To date, most cases have shown little or no response to medical treatment. Affected workers generally notice a gradual reduction or cessation of cough years after they are no longer exposed to flavoring vapors, but abnormalities on lung function tests and shortness of breath on exertion persist. Several with very severe disease were placed on lung transplant waiting lists. Workers exposed to flavorings may also experience eye, nose, throat, and skin irritation. In some cases, chemical eye burns have required medical treatment. While most workers with very severe flavoring-related lung disease have shown evidence of bronchiolitis oblliterans, it is possible that some workers exposed to flavoring chemicals may develop new-onset asthma or exacerbation of pre-existing asthma.

Disease Reporting

NIOSH is continuing to evaluate new information pertaining to the risk of obliterative bronchiolitis from occupational exposures to flavorings, in order to determine appropriate further steps to help safeguard workers' health. We want to hear from workers who have a lung problem they suspect might be related to their work with flavorings. Workers, labor union representatives, and company management at workplaces where workers may be exposed to flavoring-related chemicals can request a NIOSH health hazard evaluation of their facility. We also want to hear from health-care providers who suspect flavorings-induced occupational or nonoccupational obliterative bronchiolitis in a patient. NIOSH can be contacted to inquire about or provide information regarding lung disease that may be related to exposures to flavoring chemicals. Cases should also be reported to local and state public health departments.

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