The nation's four biggest makers of microwave popcorn have removed a flavoring chemical linked to a lung ailment in popcorn plant workers from nearly all their products. The companies say all their microwave popcorn recipes should be changed by January. But it might take several months for the reformulated popcorn to replace all the older varieties on store shelves.

In August, the Weaver Popcorn Co. of Indianapolis said it had removed the butter flavor diacetyl from all its microwave popcorn varieties. ConAgra Foods Inc. of Omaha; General Mills Inc. of Golden Valley, Minn.; and the American Pop Corn Co. of Sioux City, Iowa, all promised in September to change their microwave popcorn recipes. Those three companies sell Orville Redenbacher, Act II, Pop Secret, and Jolly Time microwave popcorn.

The chemical diacetyl has been linked to cases of bronchiolitis obliterans, a rare life-threatening disease often called popcorn lung. Diacetyl occurs naturally in foods such as butter, cheese, and fruits, and the FDA has approved its use as a flavor ingredient. Federal agencies and lawmakers have taken note of the problems with diacetyl. This fall, the House of Representatives approved a bill that would limit worker exposure to diacetyl in plants that use the chemical. The Senate has not yet considered the bill.

Learn more about butter flavoring lung injuries and the rights of factory workers allegedly injured by diacetyl.