Is it safe to microwave plastic? Heat makes it shed more

Is it safe to microwave plastic?

Microwaving is when plastic containers shed the most in lab tests. In a 2023 study, microwave heating released more micro- and nanoplastics than fridge or room-temperature storage. Source 1

That doesn’t mean one reheated lunch is a problem. It means heating is the easiest place to cut back: Harvard Health suggests moving food to glass or ceramic containers labelled for the microwave. Source 3

Where does the “billions of particles” number come from?

From that same study. Some containers released as many as 4.22 million microplastic and 2.11 billion nanoplastic particles from one square centimetre of plastic in 3 minutes of microwaving. Source 1

The researchers used water and 3% acetic acid as stand-ins for watery and acidic food. So it’s a count per patch of container in a lab. The study didn’t measure a real meal, so the figure can’t tell you how many particles were in one.

Does the cell test show harm in people?

No, it wasn’t designed to. Particles from the containers were added to human embryonic kidney cells in a dish at 1,000 micrograms per millilitre, and about 77% of the cells had died after 2 to 3 days. Source 1

The same paper’s highest intake estimate was about 20 to 22 nanograms per kilogram of body weight a day, for infants and toddlers having microwaved water or dairy from these containers. Source 1 The researchers say the health effects of eating micro- and nanoplastics “remain unclear.” Source 5

Do microwaves make food radioactive?

No, microwaves don’t make food radioactive. The FDA says microwave energy is changed to heat as food absorbs it, and “does not make food ‘radioactive’ or ‘contaminated.’” Source 2 The question is the container, not the oven.

Is “microwave safe” plastic OK?

Harvard Health says only containers that pass tests meeting FDA standards can carry a microwave-safe label. Unlabelled ones “aren’t necessarily unsafe; the FDA simply hasn’t determined whether it is or not.” Source 3

The containers in the 2023 study were made from plastics the FDA has approved, and they still shed particles in the microwave. Source 5

Harvard Health also says most takeout containers and margarine or yogurt tubs aren’t microwave-safe, plastic wrap shouldn’t touch food while it heats because “it may melt,” and old, scratched or cracked containers “may leach out more plasticizers.” Source 3

Does plastic only shed when it’s hot?

No, plastic doesn’t only shed when it’s hot. In the same lab tests, keeping the stand-ins in plastic in the fridge or at room temperature for over six months also released millions to billions of particles. Source 1 Microwaving released the most, in just 3 minutes, which is why it’s the first thing to change.

What can you use instead?

Glass or ceramic for heating, and glass for storing. The American Academy of Pediatrics advises families to “avoid microwaving food or beverages (including infant formula and pumped human milk) in plastic, if possible” and to use “alternatives to plastic, such as glass or stainless steel, when possible.” Source 4

The lid has a silicone seal ring to keep it airtight. The ring sits at the rim, and food rests against glass. Tip leftovers into a glass bowl before microwaving.