Plastic is a tricky material to use in your microwave. Some plastics will melt and degrade when exposed to the high heat and can leach undesirable chemicals into your food. Definitely something you want to avoid.
How to tell if plastic is microwave safe
You can be sure a plastic bowl, plate or container is safe to use for a microwave oven if the words “microwave safe” or “microwavable” are found somewhere on the dish.
It’s usually found on the bottom and often accompanied by a design of a microwave oven or some waves.
In the US, the “microwave safe” label is regulated by the FDA to guarantee that the manufacturer has done the necessary testing to ensure the container is microwave safe.
If there is no “microwave safe” label? It’s possible the container is still safe for use and just hasn’t been tested. But why take that risk?
Another important point is to not fall into the trap of assuming a container that doesn’t heat up is safe. The microwaves from the microwave oven will pass straight through the plastic itself, but the plastic can be heated by being next to your heated up food. This is what causes the leaching (more on this below).
Be safe, look for the “microwave safe” label.
How dangerous can plastic be?
The issue with microwaving plastic containers is undesirable chemicals and compounds leaching into the food and finding their way into the body. Of particular concern are BPA plastics.
BPA chemicals have come under fire in recent years due to a number of studies linking them to various health conditions. This article gives a far better summary than I could of the implications. Here are a couple of choice quotes.
“The two components in plastics that experts are most concerned about are phthalates and bisphenol-A (BPA), which are often referred to as endocrine disruptors because of their ability to affect estrogen and testosterone levels in humans. They also appear to have the potential to impact the development of the brain and reproductive organs in developing fetuses.”
“Exposure to BPA when a fetus is developing, meanwhile, has been associated with prematurity, changes in breast and prostate cells, early puberty, obesity, diabetes, and heart disease according to the Pediatric Environmental Health Specialist Unit.”
Given all that, is it really a risk you want to take?
What makes something microwave safe?
There are two reasons that a container or material may be considered NOT microwave safe.
- The material itself is unsuitable for heating in a microwave. For example, all metals will reflect microwaves rather than absorbing them or letting them pass through. This can cause a dangerous build up of energy.
- The material contains chemicals or constituents that are unsafe for human consumption AND these constituents could find their way into the food or liquid being heated.
In the case of plastics, it’s the second one.
In the US, the FDA stipulates a number of guidelines a container must meet in order for the manufacturer to label something as “microwave safe”.
Here’s a summary of the process, quoted from the FDA.
“Some plastics are deemed by the FDA to be microwave safe. To get the FDA’s designation, manufacturers must test the containers, estimating how long the container will be in the microwave, how much a person is likely to eat from the container, and the anticipated temperature of the food inside.
Provided the amount of chemicals leaching from the container into the food is estimated to be lower than the maximum allowable amount, the container is considered microwave safe. But that doesn’t necessarily guarantee safety.”
Interestingly, the FDA doesn’t do the testing, the manufacturer must do it themselves. Taking that into account, you may want to stick with a safer bet such as glass which will never leach into food as the melting point is far too high.
What materials are microwave safe?
Outside of a “microwave safe” label, experts advise the best materials for use in a microwave are glass and ceramic. These materials have very high melting points (3000°F or more) and will not leach into food.
Do understand that this does not mean glass or ceramic does not heat up. One common cause of accidents is picking up a scalding hot dish that can cause a burn or cause you to drop hot food everywhere. The heat can still travel from the food to the container by convection.
Metal containers are an absolute no-no. The microwaves reflect off the metal which can cause a build up of energy which will at best burn your food and make it inconsistently hot. At worst, it can blow up your microwave.
If you need to cover your food, use a paper towel rather than plastic wrap. This minimizes undesirable plastics finding their way into your food.
The worst plastics to avoid are those that are one time use. Take out boxes or margarine tubs, for example, are likely culprits for leaching plastic into food.
The types of plastic themselves have an impact. Without wanting to get too stuck in the weeds, these are the symbols you’re looking for of plastics that you want to AVOID in your microwave (and probably storing anything for human consumption as even without heat it can leach.)
The number 6 the infamous BPA chemical that you’ve surely heard about.