Is It Safe to Reuse Plastic Food Containers?

Is the fleet of plastic containers in your fridge putting your health at risk? (Photo: Getty Images/Steven Puetzer)

Between sturdy take-out boxes, margarine tubs, and inexpensive plastic containers, it’s not hard in today’s day and age to find a home for your leftover pasta. In fact, the average American woman owns 22 plastic food containers, and half of women repurpose food packaging as storage containers, according to a ShopSmart survey.

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That may sound resourceful, but among experts, it’s actually some cause for concern. In the short term, “the biggest risk is bacterial contamination,” says Rolf Halden, PhD, director of the Biodesign Institute’s Center for Environmental Security at Arizona State University. If a container is intended for one-time use, it may not be designed for easy cleaning, potentially allowing germs to proliferate the longer you hang on to it.

For example, “if you have a very narrow opening, like a soda bottle, it’s essentially impossible to clean effectively, other than pouring a boiling liquid inside to kill all the bacteria,” Halden tells Yahoo Health. “And that would compromise the plastic.” In a 2002 Canadian study, researchers tested water from elementary school students’ water bottles — many of which had been continually refilled without being washed — and found that nearly two-thirds of the samples contained enough bacteria to be rendered unfit for consumption.

But what about easy-to-clean containers, like those little plastic soup bowls from take-out joints? Although you may be able to thoroughly rinse out any food residue, that doesn’t mean you should add these containers to your lunchbox repertoire. In fact, Halden recommends transferring restaurant leftovers to a glass container as soon as you get home.

Why? Chemicals lurking in some containers — especially those that aren’t designed for reuse — could leach out of the plastic and into your food if you heat them in the microwave, toss them in the dishwasher, or leave them in the sun for a long period of time, Halden says.

But before your toss your tub, check the bottom for the recycling code, a number that can help you identify what type of plastic your container is made from. If you see #2, #4, or #5, then you’re most likely in the clear for chemicals, which means you can safely reuse your container, whether you bought it at the supermarket or brought it home from a restaurant, says Daniel Schmidt, PhD, an associate professor of plastics engineering at the University of Massachusetts.

“Most of the reusable containers you buy at the store are made of plastic #5,” or polypropylene, which has a low risk of chemical leaching, says Schmidt. (It’s also commonly used for yogurt containers, margarine tubs, and bottles for pourable foods, like syrup.)

Same goes for low-density polyethylene (recycling code #4), often used for packaging films, and high-density polyethylene (recycling code #2), from which milk jugs are made. “Plasticizers aren’t typically used in these plastics,” Schmidt says. “So the only thing you’d have to watch out for is exceeding the maximum-use temperature, just to avoid warping or deforming them.”

Related: California Has Passed a Bill That Bans Plastic Microbeads

In other words, BPA and phthalates — two of the health-threatening chemicals you’re most likely to hear about with regard to plastics — probably aren’t embedded in the containers you buy to use over and over again. The additives you’re most likely to find are antioxidants, such as BHA or BHT, which are also used in food, says Schmidt.

For the sake of caution, if you’re reusing food packaging containers — even those with “safe” recycling codes — try to limit their use to foods with similar acidity, sugar, fat, and alcohol content to the item that originally came in them, says Schmidt. (For example, don’t use a plastic shortening container to store a vinegar-based salad dressing.) And only zap ‘em if the original packaging came with heating instructions. That way, the plastic will maintain its integrity for as long as possible.

What About the Other Four Recycling Codes?

Code #1 flags PET, or polyethylene terephthalate — a name that practically advertises its chemical content. But the truth is, phthalates may not be the most troublesome component of PET containers, which include throwaway water bottles, two-liter soda bottles, some take-out containers, and peanut butter jars. “In PET, the only ‘phthalate’ is actually a terephthalate, which is a slightly different chemical structure,” says Schmidt. “It is part of the plastic — it cannot come out as an oil into your food or anything like that.”

What is more concerning is the use of antimony-containing chemicals during the manufacturing of PET. “Not all PET contains this antimony catalyst,” Schmidt says. “Antimony-free PET exists, but the consumer is not going to know which one it is by looking at it. You’d have to do chemical testing.” If you leave an antimony-laden PET container in a hot car or garage, the antimony — which has been linked to diarrhea, muscle/joint pain, anemia, and heart problems — could leach out into the container’s contents, potentially exceeding the EPA’s allowable limits, according to an Arizona State University study.

“If PET is at a low temperature, you should be fine,” says Schmidt. Read: Don’t fear PET if you place it in the fridge.

Recycling code #3 indicates polyvinyl chloride, or PVC, sometimes referred to as “the poison plastic,” since the flexible form of PVC has been shown to leach hormone-disrupting phthalates. Fortunately, you aren’t likely to find food containers made out of PVC, says Schmidt, although some plastic wraps are still made from it. (Signs your plastic wrap may be made from PVC: It’s super clingy, has a distinct odor, and has a slight purplish tint.)

If you see a #6 on your container, you’re probably looking at Styrofoam or, less often, a clear disposable takeout container, which you should toss ASAP. That’s because styrene — a possible human carcinogen — can leach into your food, though the amount is probably small. Still, “I wouldn’t microwave polystyrene — it’s not very heat resistant, even though you sometimes do get hot coffee [in a Styrofoam cup],” says Schmidt. “If something is made to be disposable, it’s made for a single use — and maybe it’s best to just use it that way. The manufacturer is presumably expecting that people are only going to use it once and may have not designed it to be used more than once.”

Related: Why You Shouldn’t Drink Warm Bottled Water

Recycling code #7 is a bit of a catch-all: Any plastic that doesn’t fall into categories #1 through #6 is labeled #7. “This can be anything, including BPA-based polycarbonate or a mixture of different materials,” says Halden. “When a consumer looks at the bottle and it says #7 recyclable, that makes it impossible to tell whether this is a bisphenol-A bottle or whether it’s some other material that fits into category #7.”

However, this category is perhaps most known for polycarbonate, a notorious BPA-containing plastic. Most of the food containers in your kitchen probably aren’t polycarbonate, which is extremely hard and impact-resistant (think of the earliest Nalgene bottles), though there are some notable exceptions still being sold in supermarkets. (Also, if you’ve been using the same containers for years — that is, long before BPA-phobia began — your containers may be polycarbonate.) “I would never put anything made out of polycarbonate in the dishwasher,” says Schmidt. “That would encourage the leaching of BPA.”

Why Be Wary of BPA?

What makes BPA so worrisome? It falls into a class of chemicals broadly known as endocrine disruptors — that is, “any manmade chemical that in some way interferes with our body’s hormones and endocrine system,” says Andrea Gore, PhD, editor-in-chief of the journal Endocrinology. Although reproductive effects — for example, decreased sperm count, increased rate of miscarriage, and early-onset puberty — are perhaps the most widely publicized risk, BPA can also bind to receptors for hormones other than estrogen (and testosterone).

There’s now evidence, for example, that BPA may interfere with thyroid hormones — and the effects could be far-reaching. “Our body needs to have normal thyroid hormone levels in order for us to have normal metabolism,” Gore says. “This isn’t simply a matter of getting fat — every cell in our body has to undergo metabolism in order to survive. Our cells need to take in oxygen, they need energy, they need to get rid of waste products. If that doesn’t happen properly, cells will die.” There may also be behavioral effects of BPA, such as hyperactivity and aggressiveness, says Halden.

From the get-go, scientists have known that BPA has hormone-mimicking properties — it was originally discovered by pharmaceutical companies trying to develop estrogen-like drugs. As it turned out, “BPA is pretty weak at activating the estrogen receptor, so it was thrown away as a pharmaceutical,” Gore says. “BPA is not a very good estrogen but it’s a very good plasticizer. So it ended up making its way into plastics.” If its hormonal effects are weak, why does exposure to BPA even matter? At certain ages, children aren’t naturally exposed to any estrogen, making even a small amount of exposure significant. And over time, if you’re exposed to the chemical day after day, the hormonal effects can add up, even in adults.

And BPA has been shown to migrate out of plastic: A 2013 study in the journal Environmental Science & Technology, for example, found that the more water people drank from polycarbonate bottles, the higher their BPA levels tended to be. The study was conducted during the hottest months of the year, leading the researchers to conclude that sun exposure caused the chemical to leach from the bottles into the water — an effect that could be replicated by microwaving potentially problematic plastic, especially if the food you’re zapping is oily or fatty, says Halden.

“If you tested everybody in the U.S., Canada, and most of the industrialized world, you would find BPA in something like 95 percent of people’s urine,” says Schmidt. “BPA has a biological half life of about a day, so that means we’re all being constantly exposed to it.” (Keep in mind, plastic containers aren’t the only culprit: A major source of BPA exposure is the epoxy lining in canned foods.)

Luckily, BPA is being increasingly phased out, which means most containers designed for reuse are free of the chemical. “If you do a sensitive-enough test, eventually you will find something,” says Schmidt, which may explain, at least in part, why an often-cited study detected endocrine disruptors in every type of plastic tested. What’s going on? Cross-contamination can occur during manufacturing, leaving even BPA-free containers with traces of the stuff, as well as other chemicals.

“Can you guarantee there’s not a single molecule of BPA or a phthalate in something? Probably not,” says Schmidt. “But that shouldn’t be the sole concern. In the grand scheme of things, the hazards that could potentially be associated with reusable plastic food containers may be outweighed by other things we have to worry about — for instance, what food is in those containers and how much of it we eat.”

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