The Reason You Pop Popcorn 'This Side Up'

microwaved bag of popcorn being poured into glass bowl

Treehugger / Alexandra Cristina Nakamura

Movie night at home. Time to break out the microwave popcorn and settle in for the show. It's so automatic — and convenient — you probably don't give these microwaveable munchies much thought. But have you ever wondered why the bag says "This Side Up," and what would happen if you did it the other way instead? What's actually inside the bag before it's popped? And is microwave popcorn even healthy?

The answers aren't simple, and some may surprise you. Here's everything you need to know about the microwave version of this enduring snack.

Does it matter which side is up?

unpopped instant popcorn bag inside black microwave, ready for heating

Treehugger / Alexandra Cristina Nakamura

The short answer is yes, and here's why. Inside the microwave bag, you'll see a silvery gray rectangle called a susceptor on the "down" side of the bag that's supposed to lie on the glass microwave tray. This metalized polymer film, used in a lot of microwaveable packaging and crisping sleeves, absorbs the microwaves and heats things high enough to cook the popcorn kernels via conduction.

The reason the susceptor isn't on the "up" side is because the kernels are supposed to be positioned over the silvery film, not beneath it. What would happen if you microwaved popcorn with the susceptor side up? Rest assured, your bag wouldn't explode or burst into flames. And your popcorn would still pop — just not as many kernels and the popped ones might be unevenly shaped.

Are susceptors safe?

person reads book on rug with clear glass bowl of popcorn nearby

Treehugger / Alexandra Cristina Nakamura

The FDA says that when hot oil comes in contact with a susceptor, it can release volatile chemicals that may be absorbed in the oil and food in small amounts.

There's not a lot of research on susceptor safety. But one study published in the Journal of AOAC International tested several microwave food products packaged with susceptors and discovered they emitted many potentially dangerous volatile chemicals in small amounts, mainly from the adhesive and paper that often overlays the susceptor. This included the carcinogen benzene found in three products. On a positive note, the study found no product contained all the chemicals and indicated that many susceptors have since been reformulated to remove the trace amounts of benzene.

Even so, eating microwave products with susceptors on a frequent basis may not be your healthiest option.

What's inside the popcorn bag?

hands shows off opened bag of unpopped microwave popcorn with compacted butter and kernels

Treehugger / Alexandra Cristina Nakamura

Open an unpopped bag and you'll find a compacted cake of stuck-together kernels, solid oil, preservatives and flavorings. Not exactly appetizing, but it's engineered that way for optimal popping above the susceptor.

Is it bad for you?

man holds handful of popcorn to open mouth

Treehugger / Alexandra Cristina Nakamura

Popcorn on its own is actually pretty healthy — one of the few snacks that's whole grain, low in calories and high in fiber, particularly when it's popped with minimal oil and butter. Trouble is, when you opt for the microwaveable kind it typically contains lots of unhealthy artificial flavorings and fats.

Of particular concern are the potentially risky chemicals used to make microwave popcorn taste buttery. Manufacturers once relied on a compound called dicetyl, which turned out to cause "popcorn lung" in workers who inhaled it day after day at factories. Many companies have switched to healthier alternatives, though at least one butter flavor substitute, 2,3-pentanedione, has been shown to do similar damage to the respiratory tract. It can be virtually impossible to tell what chemicals you're getting because the FDA only requires the label to say "artificial flavorings." If you're worried about toxic flavorings, forgo butter-flavored microwave popcorn. If you can't give it up, don't inhale steam from the popcorn bag.

Another concern is the use of unhealthy partially hydrogenated oil. It's often added to keep the block of kernels and flavorings solid at room temperature, but it contains trans fats that boost your risk of heart disease. Even though the FDA recently restricted the use of trans fats in foods, some companies have found a loophole that lets them claim their products don't contain any if they keep the amount below half a gram per serving. Look for trans-fat-free popcorn brands like Newman's Own and most Orville Redenbacher's varieties.

One caution: Although microwave popcorn companies have phased out most trans fats, many now rely on palm oil, which is high in heart-harming saturated fat. Choose brands labeled low-fat or those that keep saturated fat to 1.5 grams per 5 cups or less.

What about the bag itself?

hand puts used microwave popcorn bag into black trash can

Treehugger / Alexandra Cristina Nakamura

Materials in the bag are also worrisome. The good news is that, as of 2016, the FDA no longer allows the lining of microwave popcorn bags and other food packaging to contain a chemical called perfluorooctanoic acid (PFOA), which makes them grease resistant but is linked to many cancers, infertility and birth defects. The bad news is that the FDA has since approved almost 100 PFOA-like substances for use in food packaging, most of which haven't been studied for their effect on human health.

Forgo the microwave

popcorn being popped in sauce pan on gas stove ,the old-fashioned way

Treehugger / Alexandra Cristina Nakamura

To avoid these microwave popcorn pitfalls, consider popping your own the old-fashioned way — on your stovetop. Make it extra healthy by forgoing the oil and butter. Use flavorings like paprika, cumin or parmesan cheese instead. Learn how here.

Another oil-free option is to use an air-popped popcorn machine. Or if you prefer microwave popcorn, opt for healthy brands. Or try popping your own healthy, chemical- and oil-free microwave version in a brown paper bag at home.