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In Too Afraid to Ask, we’re answering food-related questions that may or may not give you goosebumps. Today: Can you put plastic in the microwave?
It all started by accident. Kazi Albab Hussain, a PhD student at the University of Nebraska–Lincoln, was studying silver nanoparticles released by certain types of plastic food packaging when he noticed another confetti-like substance under the microscope: tiny plastic bits.
As a new father he became preoccupied by the discovery. “I’d been exposed to a whole new world, and I was worried to see that a lot of baby foods were stored in plastic,” he says. So Hussain shifted gears in his research. He wanted to know: Just how many of these particles was his child eating?
Quite possibly billions, according to his findings. To test materials widely used in baby food packaging, Hussain brought a couple of store-bought polypropylene-based reusable plastic containers and a polyethylene-based reusable plastic food pouch back to his lab. Along with his team, he filled the storage vessels with water and 3% acetic acid to mimic the aqueous and acidic foods they might reasonably contain in real life. After storing the filled containers in the fridge or at room temperature for 10 days, the team found millions to billions of microplastics and nanoplastics in the liquids.
Microwaving the containers accelerated the process by an alarming magnitude: Within three minutes, some containers released as many as 4.22 million microplastics (particles smaller than 5 millimeters) and 2.11 billion nanoplastics (particles about 70 times smaller than the width of a human hair) per square centimeter of surface area. Hussain’s research indicates we’re eating a lot more plastic than previously believed. In 2019 one study calculated we might be ingesting about 50,000 microplastic particles per year.
The health impacts of eating plastic is still unclear, but researchers have long suspected they’re not great. And growing evidence suggests high exposure to microplastics (and the lengthy list of chemicals they’re made from) could provoke immune and stress responses, along with various reproductive, metabolic, and behavioral issues.
Given the mounting concern around one of earth’s most-produced substances, Hussain’s findings beg a timely question: Can you put plastic in the microwave?
Microwaving plastic can release harmful chemicals like BPA and phthalates into your foods and drinks. Therefore, you should avoid microwaving plastic, unless it’s labeled for this specific use.
What does microwaving do to plastic?
Plastics are spaghetti-like chains of carbon molecules, called polymers, which are usually derived from crude oil. To make plastics that are clear, cloudy, rigid, or soft, manufacturers add a cocktail of chemicals. Though there are more than 10,000 of them, the most well-studied groups are: bisphenols (which include BPA and are often found in rigid products, like food storage containers and water pipes) and phthalates (which are typically used to make more flexible products, such as food prep gloves or the plastic lining inside a milk carton).
As Hussain found, microplastics and chemicals can build up in your leftovers over time—even when you’re storing those plastic containers in the fridge. But microwaving wet foods in plastic delivers an even bigger one-two punch: Heat speeds up hydrolysis, the process by which water molecules can essentially break chemical bonds apart. This supercharged reaction causes plastic containers to shed microplastics and nanoplastics, as well as leach chemical additives (the bisphenols, phthalates, and more), into your food. And once those microplastics are ingested, it’s possible they can degrade and also leach chemicals in the body.
In other words, heating plastic essentially makes it softer and more porous. If you’ve ever microwaved marinara sauce in a plastic bowl, you’ve seen the sunset red, impossible-to-remove stain it leaves behind. “Passages in the plastic can open up, so the sauce gets inside,” says James Rogers, PhD the director of food safety research and testing at Consumer Reports. The opposite exchange happens too: “If something goes in, something can also come out,” he says.
Are those chemicals and microplastics unsafe?
Just about all Americans have measurable amounts of phthalates and BPA in their bodies. Mammalian animal studies strongly suggest that, once inside, these chemicals act like sneaky gatecrashers at a masquerade ball. They’re not welcome at the party, but they’re also tough to parse from the legitimate guests.
That’s because bisphenols and phthalates are endocrine disruptors. They can mimic, block, or interfere with the body’s hormones—possibly increasing the risk of various conditions, including infertility, some cancers, metabolic diseases, neurological conditions, and immune system dysfunction. According to Laura N. Vandenberg, PhD, a professor of environmental health sciences at the University of Massachusetts Amherst, “That’s just the short list.”
Various human studies have also reinforced the animal ones. Exposure to high phthalate levels in the womb has been linked to asthma in childhood. For boys, that early contact could cause behavioral problems as well as potentially lower sperm counts later in life. Pregnant people might experience lower thyroid hormone levels and more preterm births.
There’s a lot more that we don’t know. At Duke University, Jason Somarelli, PhD, the director of research at the Duke Comparative Oncology Group, is studying the thousands of other additives in plastics. “We’ve found at least 100 known carcinogens in these other chemicals,” he says. “And then there’s well over 2,000 others where we just don’t have enough data to know.” What he can say with confidence: “There’s bad stuff in plastic.”
Beyond the chemicals being leached by plastics, the particles themselves—which have been discovered in human hearts, bloodstreams, lungs, placentas, semen, and breastmilk—pose a threat too. The body sees the physical particles as intruders, so naturally they seem to fight back. That can trigger an immune response: Because plastics can’t be degraded, white blood cells die in the battle, causing inflammation. Those particles can also “act as transport vehicles for other pollutants,” says Vandenberg, bringing potentially toxic substances into the body.
Hussain wanted to see for himself what microplastics and nanoplastics might do inside our bodies. His team bathed human embryonic kidney cells in high concentrations of plastics shed by the containers they were testing. Within 48 hours, 76% of embryonic kidney cells died—about three times more than the percentage of cells that spent the same amount of time in a more diluted (less plastic-y) solution. Hussain’s findings corroborate another study published last year, which determined that direct microplastic exposure can cause cell death, inflammation, and oxidative stress.
So, why aren’t the cells in our bodies dying en masse? “The big outstanding question is uptake,” says Somarelli. “If these plastics just get in our guts and we flush most of them out—if we’re all just walking around pooping and peeing out plastic all the time—then they will have potentially little effect.” That’s what Hussain hopes is happening too: “I would like to believe that our body is working on getting them out,” he says. But even if these particles and chemicals aren’t making us sick immediately, most experts I spoke to suspect they could still have longer-term effects.
Don’t Microwave Food in Plastic Containers!
FAQ
Is #2 plastic microwave safe?
Can you put plastic 2 in the microwave?
What happens if you accidentally microwave plastic?
What are the effects of microwaving plastic?
Is microwaving plastic bad for You?
Second, endocrine-disrupting chemicals can leak (or, more formally, “leach “) from plastics and soak directly into your food. Microwaving plastic only makes matters worse; both the shedding of microplastics and the leaching of chemicals become more likely when plastic is heated.
What are the dangers of eating microwaved food?
With regard to the nutritional quality of food, it is important to note that any heating method can lead to the loss of heat-sensitive nutrients. This includes heating in the microwave, conventional oven or any other method. Apart from that, there is no scientific evidence to prove any other harm to health caused by the use of microwaves.
Does microwaving food in plastic containers affect human health?
But microwaving food in plastic containers might increase the likelihood that harmful chemicals or microplastics come into contact with your meal. Their impact on human health is not yet well understood. [Credit: Brad.K | CC BY 2.0]
What happens if you microwave food in plastic?
Condensation underneath the plastic wrap, which could contain phthalates, could cause fluid to drip down into the food, Halden says. If microwaving food in plastics is unavoidable, then pay attention to the recycling codes at the bottom of the container. Those codes say something about the type of plastic used—avoid any that have the code 3 or 7.