The introduction of microwave popcorn during the 1980s seemed like a natural progression after the success of stovetop popcorn and air-popped popcorn. A consumer would place a folded bag containing oil, flavoring and popcorn kernels into a microwave oven for a few minutes. The results could be variable, from a half-popped bag to a smoking bag of carbon, but in general, microwave popcorn was similar to other forms of popcorn, and done in much less time.
Questions over the safety of microwave popcorn began to arise when a number of popcorn factory workers started reported severe respiratory problems while working with the chemicals used to process the popcorn. Specifically, a chemical known as diacetyl was the suspected irritant. Diacetyl is used to create a buttery flavor in various seasonings and processed foods, including the artificial butter flavor used for microwave popcorn. Small amounts of diacetyl are not considered toxic, but when heated on a factory scale the fumes can trigger a respiratory condition known as popcorn lung.
When word of the popcorn workers' exposure to diacetyl became public, many health professionals became concerned over the safety of microwave popcorn at the consumer level. The FDA and other agencies determined that the amount of diacetyl contained in an average bag did not reach toxic levels, although critics questioned the validity of these findings after discovering little to no testing had actually been conducted on a consumer level. Virtually all reported cases of popcorn lung occurred in popcorn factory workers, but one consumer who ate two bags of popcorn every day and habitually smelled the fumes did contract a milder form of the disease.
If there is any danger at all associated with microwave popcorn, it is most present when the bag is first opened and heated fumes escape. Breathing in these fumes will expose the consumer to the highest level of diacetyl possible at the consumer level. This may cause damage to the smallest air passages in the consumer's lungs or trigger a pre-existing asthma attack. Young children and those with compromised lung capacity may also have an adverse reaction after breathing in the first fumes of a hot bag of microwave popcorn.
Other ingredients contained in microwave popcorn are not considered toxic, although some health experts would warn against consuming high levels of sodium or partially hydrogenated oils. It generally uses healthier oils that certain movie-style popcorn served in theaters or concession stands. Avoiding the addition of artificial butter or extra salt is always a good idea for a healthier snack.