For some of us popcorn fanatics, it’s almost sinful to think of gnoshing without the butter. Unfortunately, the “butter” in many popular microwave popcorns isn’t butter anyway. Instead, it’s a blend of chemicals that mimic the flavor of the real stuff.

Recent concerns over the safety of those butter flavorings has led the National Institute of Environmental Health Sciences (NIEHS) to delve further into the ingredients behind the flavor. One ingredient in particular, diacetyl, has been linked to obliterative bronchiolitis (OB), a very rare but debilitating lung disease. Workers in microwave popcorn factories seem to develop OB in suspicious numbers.

To study the effects of breathing diacetyl-filled air, researchers exposed laboratory mice to air filled with diacetyl vapors in amounts similar to that which a factory worker would breathe during the normal course of work. After just three months, the mice began developing lymphocytic bronchiolitis, a harbinger of OB. None of the mice developed a case of OB, however.

Researchers suggest the presence of lymphocytic bronchiolitis but no OB may be due to anatomical differences between mice and humans. Mice breathe exclusively through their noses but humans also breathe through the mouth.

There is speculation that the noses of the mice process toxic vapors in a way that may prevent the toxic vapors from going deeper into the respiratory system. The bronchioles, tiny airways in the lungs, are where the obstruction in human lungs occurs.

When diacetyl vapors were administered to the mice in a manner that bypassed their noses, they developed lesions in the bronchioles that did partially obstruct these delicate airways. Further study is under way to determine if the obstructions progress to the point of OB development in the mice.

Plans for larger studies are being developed to extend the field of toxicity data on diacetyl in artificial butter flavorings, as well as that of another major flavoring component, acetoin. The National Toxicology Program, part of NIEHS, will conduct the additional studies.

The details of the current study can be viewed online at the website for the journal, Toxicological Sciences.