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Even though Wayne Watson was so short of breath he struggled to sing his solos in the church choir, he was stunned earlier this year to learn what may have caused his serious lung disease. "You would never think of popcorn being a dangerous substance," says the 54-year-old furniture salesman from Colorado. Watson was diagnosed with bronchiolitis obliterans (popcorn lung), a potentially deadly condition that had previously been linked, not to consumers but to popcorn factory workers with high-level exposure to diacetyl, an additive used to give the ubiquitous snack its buttery flavor. Watson had eaten two bags of extra-butter microwave popcorn a day for 10 years. But more critically, say experts, he breathed in the buttery aroma each time, bringing diacetyl to his lungs. "I'd tear open the bag, and those fumes would hit me," says Watson. His lung function dropped sharply but has partially rebounded since he gave up popcorn. Concerned about safe snacking? Here are answers to your questions.

Is microwave popcorn a health risk?
Not when eaten, experts agree. The potential risk is from inhaling large quantities of the vapors produced when corn is popped. Says John Hallagan of the Flavor and Extract Manufacturers Association of the United States: "It's only dangerous when it's heated up enough to become a gas you can inhale [190°]."

Is getting a whiff of freshly popped corn a problem?
No. "The risk is very low," says David R. Lineback, retired director of the University of Maryland's food safety institute. But to be extra-careful, don't stand next to the microwave or open the bag under your nose. Once poured into a bowl, the snack is safe.

What is diacetyl?
A substance that gives butter its flavor. It's found naturally in many foods—dairy products, coffee and some vegetables and fruits such as strawberries—but is used in higher concentrations as an additive to products like cake mixes and frozen foods. Microwave popcorn has the highest diacetyl content of all products.

How do I know if diacetyl is in my popcorn?
It can be hard to tell, since the chemical is not always named as an ingredient. Look for butter flavoring. The manufacturer of the brand Pop Weaver has already removed diacetyl from its microwave popcorn; others, including those who make Orville Redenbacher, Pop Secret, Act II and Jolly Time, say they will eliminate diacetyl in the near future. For now, unless the product is marked diacetyl-free, assume it contains the additive.

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