Say goodbye to the shiny stuff. Food safety experts explain why there are safer ways to store your leftovers.
You didn’t finish dinner, so you cover the scraps with some aluminum foil before stashing them in the fridge. And if you’re anything like us, you’re working on autopilot—the leftover game is the same whether you’re at mom’s house (eagerly!) accepting meatballs or at home wrapping that last slice of pizza. As long as my food has that shiny shield over it, we think, what could possibly go wrong?
A lot, actually. To get to the bottom of it, I reached out to a professor of public health and a registered dietitian, who answered my most pressing questions: Are we wrapping our leftovers all wrong? Does it matter which side of the aluminum foil faces up? Is it bad for the environment? Or worse, is aluminum foil toxic to our health?
If you have a nagging feeling that you’re storing leftovers the wrong way, you’re in the right place. Read on to find out the unexpected problem with wrapping scraps in aluminum foil and the better way to store your second-day meals.
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What is aluminum foil?
You’d know it anywhere, but what, exactly, is it? Aluminum foil is, as the name suggests, mostly aluminum—98.5% of it, combined with iron and silicon to prevent puncture, according to the United States Department of Agriculture (USDA). The manufacturers press it between rollers to get it thin.
As you’ve no doubt noticed, it has a shiny and matte side, but it doesn’t matter much which you use. The exception: when you’re using the “nonstick” kind to reheat food, in which case you should go with the dull side because it has a stick-proof coating.
Why should you avoid using aluminum foil for leftovers?
There are a few problems with wrapping leftovers in foil, and they all involve food safety.
Is aluminum foil toxic? Which leftovers are most at risk? Do you really need new food-storage containers? Ahead, we’re tackling those topics, plus why you should avoid pulling out the foil for your dinner scraps.
It can cause bacteria to grow faster
The aluminum foil itself won’t hasten bacterial growth, but the way it covers dishes can. After all, when you drape foil over a plate, even if you carefully crimp it, it doesn’t form a tight seal, so air gets in. “The lack of an airtight seal makes it easier for certain bacteria to grow more rapidly,” says Angel Luk, RD, a registered dietitian in Vancouver.
Staph (sometimes found in meats and poultry) and Bacillus cereus (found in leftover rice and other starchy foods) are two kinds of bacteria that need air to grow and multiply. And these two germs are not killed by reheating food to high temperatures, so they’re particularly dicey, Luk explains.
It traps heat, which speeds up spoilage
There’s a reason we spread foil over a tray of steaming chicken cutlets while waiting for the vegetables to cook: Foil keeps things warm. But what’s good for your dinner prep is bad for safe food storage.
“Foil traps more heat than plastic wrap or coated wax paper, and that can make your leftovers spoil quickly,” Luk says. If you cover dishes in foil before they’ve fully cooled down, the foil can trap some heat, causing the food to stay in the danger zone of 104 to 140 degrees Fahrenheit, where bacteria proliferate. “If using foil to store leftovers, I would recommend it for items that have already cooled down completely or were cold to begin with,” she says.
It can put you at risk for botulism
Here’s a surprising one: Baked potatoes stored in aluminum foil have caused cases of botulism food poisoning. The microbe Clostridium botulinum releases a toxin that can harm the central nervous system and even be fatal. “Potatoes with skins on should never be stored wrapped in foil, as this can lead to botulism poisoning,” says Jill Roberts, PhD, MPH, a professor in the College of Public Health at the University of South Florida in Tampa.
There are two problems with storing potatoes encased in foil. The first is that Clostridium botulinum bacteria multiply in low-oxygen conditions. Wrapping a potato in foil cuts the oxygen, which is just what that bad bacterium wants. The other concern with second-day spuds? Potato skin is dirty (yes, even if you scrub it before cooking), which sets the stage for trouble. “You should not save baked potatoes with the skin on, as the skin harbors dirt and therefore the microbe,” Roberts says.
Don’t worry: You can still eat the skin of a potato—right after cooking it, that is. Botulism is more likely to occur with older potatoes, like leftovers you’ve stashed in the fridge, than ones you’ve recently pulled out of the oven. That’s because bacteria have time to multiply. While storing a potato at the right temperature slows this process a little, wrapping it in foil pushes it into the danger zone.
Aluminum might leech into your food
Acidic meals like baked ziti with tomato sauce can cause foil to degrade, potentially letting aluminum leech into your food, Roberts says.
So is aluminum foil toxic—or is that just an internet rumor? Aluminum itself is a known neurotoxin. It can accumulate in the brain and central nervous system, and there’s some evidence that people with Alzheimer’s disease have more of it in their brains, according to a 2023 report in the International Journal of Molecular Sciences.
Before you panic, know this: The biggest concern comes from cooking acidic foods in aluminum foil; there isn’t great evidence that wrapping foods with it causes a significant problem. As long as your leftovers are low in the dish and the foil doesn’t touch them, it’s not a health concern, Roberts says. But if there’s any chance your wrap might brush your chili or chicken piccata, reach for plastic wrap or a container instead.
What happens if you wrap leftovers in aluminum foil?
You could get sick from food poisoning. This is especially a concern for certain populations, such as kids under 5 years old, seniors, pregnant women and anyone with a weakened immune system, Luk says.
That said, don’t worry if you have to grab some aluminum foil to transport a dish home from a potluck or need to quickly wrap your sandwich in foil because it’s all you have on hand. Everything in moderation. “I don’t want anyone to have anxiety over using foil sometimes,” says Luk. (She admits to occasionally reaching for it herself.)
What are the best food-storage options?
The safest way to store most foods is in airtight containers with lids or sealed storage bags, according to the Food and Drug Administration (FDA). These are the best for most types of leftovers because they delay the spoilage process.
There are exceptions, of course. You should never store foods that could give you botulism—such as raw vegetables, potatoes and sweet potatoes, and homemade garlic- and onion-based salsas and dressings—in airtight containers. Remember, the lack of oxygen is the perfect breeding ground for Clostridium botulinum. And be sure to throw out these leftovers promptly (more on that below).
As for the type of covered food-storage containers to use, the choice is yours. While glass may be better for the environment, when it comes to microbial growth, glass and plastic are equal, Roberts says.
“The single most important thing is to place prepared foods in the refrigerator (or freezer) no more than two hours after they are prepared,” Roberts explains. “The second most important is to discard leftovers within three to four days (if refrigerated) or six months (if frozen).”
How long can you keep leftovers, anyway?
As Roberts notes (and the USDA agrees), you can generally keep leftovers for three to four days in the fridge. Pop them in the freezer, and they’ll last three to four months, according to the USDA—even up to six months, says Roberts.
A big caveat: Some foods spoil sooner than others, so it’s key to know how long your specific leftovers will last in the fridge. You can refrigerate cooked beef or chicken for up to four days, for instance, but you should hang onto sushi for only a day or two … and that may even be pushing it. When in doubt, reference the FDA’s handy chart, which spells out food storage time frames.
About the experts
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At Reader’s Digest, we’re committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers’ personal experiences where appropriate. We verify all facts and data, back them with credible sourcing and revisit them over time to ensure they remain accurate and up to date. For this piece on whether aluminum foil is toxic, Lisa Lombardi tapped her experience as a longtime health reporter and the author of What the Yuck?! The Freaky and Fabulous Truth About Your Body to ensure that all information is accurate and offers the best possible advice to readers. Read more about our team, our contributors and our editorial policies.
Sources:
- Jill Roberts, PhD, MPH, professor in the College of Public Health at the University of South Florida; email interview, Nov. 3, 3025
- Angel Luk, RD, registered dietitian in Vancouver, co-founder of Food Mysteries nutrition consulting and author of You Can’t Out-Train a Bad Diet; email interview, Nov. 3, 2025
- U.S. Department of Agriculture: “How is Aluminum Foil Made?”
- U.S. Food & Drug Administration: “Are You Storing Food Safely?”
- Cleveland Clinic: “Botulism (Clostridium Botulinum)”
- U.S. Food & Drug Administration: “Refrigerator & Freezer Storage Chart”
