There are two safety issues involving the chemicals added into many brands of microwave popcorn. The first stems from the use of diacetyl in artificial butter flavor. Diacetyl has been linked to a rare type of lung disease, bronchiolitis obliterans, also called "popcorn worker's lung" because it has been seen primarily in workers at microwave popcorn factories. This disease destroys the lungs and can be cured only by a lung transplant. Diacetyl appears to damage lungs when it is repeatedly inhaled in vaporized form  Diacetyl does its damage when inhaled, not when it is eaten.

The other safety issue has to do with the chemical PFOA (perfluorooctanoic acid, also known as C8), used in the lining of microwave popcorn bags. PFOA is also used to make Teflon and other stain-and stick-resistant materials including pizza boxes.  Animal studies have identified four types of tumors in rats and mice exposed to PFOA.  The chemical has been shown to cause cancer and birth defects in animals

 Actually, it’s not popcorn, per se, that people should be worried about. It’s the microwave bag in which it cooks that many experts say is the problem.  The problem is the chemicals used in the lining of the bag, including perfluorooctanoic acid (PFOA).

PFOA is also used to make Teflon and other stain- and stick-resistant materials, including pizza boxes. It’s part of a number of compounds that have caused liver, testicular and pancreatic cancer in animals. The chemicals may also be linked to infertility in women, according to a recent study at the University of California, Los Angeles.

Earlier this year, a study found that these chemicals may prevent childhood vaccinations from working properly. Children who had higher concentrations of the chemicals in their blood had a lower level of protection against some childhood diseases for which they had been vaccinated.

The chemicals in the bag lining get into our bloodstream because they vaporize and migrate into the popcorn during microwaving, said Olga Naidenko, a senior scientist for the Environmental Working Group. “They stay in your body for years and accumulate there,” she told Prevention magazine for an article titled, “7 Foods That Should Never Cross Your Lips.”   The chemical is so pervasive that it’s detectable in the blood of 95 percent of Americans.

Popcorn with artificial flavoring is also a concern. A few years ago, microwave popcorn was slammed for the use of diacetyl in its artificial butter flavor, which caused a rare type of lung disease among workers who inhaled it at microwave popcorn factories.

Most manufacturers have removed diaceytl from their products, but it’s been replaced with other kinds of butter flavoring that some government scientists say are just as bad as the original stuff.

Even the top lawyer for the flavoring industry has said that “these so-called substitutes are diacetyl.”   At every supermarket in the country, microwave popcorn sells for at least $4 a pound and usually closer to $6. Ordinary popcorn is about $1 a pound, or less; good organic popcorn is about $2 a pound.