Diacetyl, a flavoring chemical in popcorn, has been linked to bronchiolitis obliterans, a rare life-threatening disease coined 'popcorn lung.' The disease has stricken some microwave popcorn plant employees who inhaled diacetyl vapors when mixing large batches of flavors. Hundreds of popcorn lung lawsuits are pending, and millions have been awarded in confidential settlements.

The average microwave popcorn consumer is not believed to be at risk, although earlier in 2007 the first case of the disease was reported in a consumer who inhaled microwave popcorn fumes several times a day for years. The Flavor and Extract Manufacturers Association states there's no worry for consumers as long as popcorn bags are opened away from the face.

Now the four biggest microwave popcorn manufacturers, Weaver Popcorn Company, ConAgra Foods, General Mills and American Pop Corn, have removed the flavoring chemical diacetyl from nearly all their product recipes. But diacetyl may still be lurking on the shelves. Stores will sell the old popcorn product first.