8 Things You Should Never Microwave

Some of the things you should never microwave are aluminum foil, frozen meats and metal utensils. We tell you more!
8 Things You Should Never Microwave

Last update: 03 March, 2023

While it’s true that the microwave gets us out of trouble in no time, there are a number of things you should not use inside this appliance. This is not only because they can damage it, but also because they can harm your health.

To clarify any questions or doubts you may have as to what you can really put in the microwave, in this article, we’re going to tell you what those things are and the reason why you should never put them in the microwave again. Keep reading, because your future health will thank you!

What are the things you should never microwave?

Read the following list and make sure you don’t make the mistake. We’re going to tell you what are those 8 things you should never (yes, never) use in the microwave. If you do, you could expose yourself to different risks, such as the following:

  • Starting a fire
  • Spoiling your food
  • Causing you to get sick

With that said, let’s take a look at the list of things you should never put in the microwave.

1. Styrofoam containers

If you ordered a food delivery the night before, please don’t reheat what’s left in the package, especially if it’s made of Styrofoam. If it comes into contact with the heat emanating from the microwave, this material undergoes chemical changes that are dangerous.

The least serious thing that can happen is that it melts and sticks to the food or the walls of the microwave. However, this material also releases chemicals that are hazardous to your health and will permeate your food.

Although there are some boxes made of this material that have a microwave-safe mark, it’s best to take your food out of the box and heat it without the packaging. This is because polystyrene is considered to be a possible carcinogen, as explained by the organization Children’s Environmental Health Network.

Los empaques de espuma de poliestireno son muy comunes y es normal que desees calentar la comida en ellos, pero no debes hacerlo.
Styrofoam packaging is very common and it’s normal that you may want to heat food in it, but you absolutely shouldn’t.

Do you like this article? Check out these: Microwaved Mushrooms: A Quick and Easy Recipe

2. Plastic

It’s common to organize some foods in plastic bags or containers, as is the case of frozen fruits and meats. Well, although this practice is valid, plastic is one of the things you shouldn’t put in the microwave.

Specifically, we’re talking about those bags and containers such as butter, yogurt, or condiments, that tend to melt when in contact with heat. There are others that are suitable for use in the appliance, such as those marked with the triangular emblem and have the numbers 2, 4, and 5.

In addition to this number, if they are really safe for use in the microwave, they should have an icon with three waves. This way you will know with greater certainty that it is suitable. In the case of plastic bags, none are safe to expose to heat, so be very careful.

3. You should never microwave metal utensils

Metal is another thing you should not use in the microwave. This is because it can seriously damage the appliance.

The appliance generates electromagnetic waves through an electron tube. The food absorbs these waves and heat is generated, which does not happen with metal, which is a conductor.

This ends up in a probable fire that will damage your appliance and affect your integrity. This applies to spoons, knives, forks, pots, and glasses with metal parts, among other utensils. Something similar applies to travel mugs because they’re usually made of stainless steel or plastic.

Only if you have a ceramic travel mug can you heat its contents in the microwave.

Metales son cosas que no se deben usar en el microondas.
Metal must not be introduced into the microwave in any way; neither should utensils or food containers. The risk of these materials causing a fire is high.

4. Aluminum foil

Aluminum foil is great for wrapping and storing food. However, i’is not recommended to heat food in the microwave with aluminum foil. As with metal utensils, it can cause sparks and damage the appliance or cause a serious fire.

Also, although some people believe that food heats up faster when wrapped in aluminum foil, in reality, the opposite is true! According to the U.S. Food and Safety Inspection Service (FSIS), the material makes it difficult for food to absorb microwaves, thus preventing heat from reaching it.

Following the principle that aluminum foil prevents food from heating, there are some recipes that indicate that it should be used to avoid cooking the ingredients completely. Therefore, the FSIS indicates that the reaction of the aluminum foil while inside the microwave should be monitored very carefully.

You should never put aluminum foil in a microwave or try to heat food wrapped in foil this way.

5. Never microwave cardboard boxes or paper bags

One of the alternatives that have become popular for packing food without using single-use plastics is cardboard boxes and paper bags. Well, that brings us to another of the things you should not use inside the microwave.

Why is this? Well, cardboard food boxes usually have a steel or plastic coating to prevent them from falling apart when containing certain products. In this specific case, you should avoid putting them in the microwave, especially if they have aluminum or metal parts.

If you see that your boxes do not have the aforementioned coatings and have the symbol suitable for heating in this appliance, do it without exceeding 60 to 90 seconds. After this time, it can be dangerous and cause a fire. The same goes for paper bags.

Las cajas de cartón y las bolsas de papel pueden quemarse y afectar la integridad de tus alimentos.
Cardboard boxes and paper bags can burn and affect the integrity of your food.

6. Old metal tableware

Old metal tableware – and even some ceramic types – that’s more than 40 years old may have traces of lead and other heavy metals in the glaze. These pose a serious health hazard, as the compounds are transferred to the food when subjected to microwave heat.

We think you may also like to read this article: Is Heating Plastic in the Microwave Safe?

7. Hot peppers

We know it’s tempting to add a couple of hot peppers to a meal and microwave it. However, subjecting these foods to a high temperature will release the capsaicin they contain.

According to scientific studies, the compound causes irritation and burns on mucous membranes. You may open the microwave door when heating hot peppers and the hot gas with the capsaicin may reach your eyes and nose and pose a health risk.

In this case, you should heat the preparation first, and then add the peppers.

Never microwave chili peppers.
You should add hot peppers after heating your meal in the microwave to avoid the irritating effects of capsaicin.

8. Never microwave frozen foods

Finally, don’t microwave frozen foods. Doing so may seem like a simple alternative to defrost meats or sausages, but the result is uneven and can be dangerous.

If we talk about ground meat, for example, you will achieve a good level of cooking on the periphery, but inside, the picture may be different. Studies indicate that the ingestion of raw meat increases the risk of contracting parasites, such as Toxoplasma gondii and Trichinella spp.

What other things should you not put in the microwave?

In addition to the 8 things we mentioned, you shouldn’t microwave cups or glass containers that aren’t certifiably suitable for this appliance. Nor should you turn it on empty. That’s right: running the appliance with nothing in it can cause a fire or damage it.


All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.


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  • Cooking with Microwave Ovens. Food Safety and Inspection Service. U.S. Department of Agriculture.
  • Espuma de poliestireno: alternativas más seguras. Children’s Environmental Health Network.
  • Fattori, Victor, Miriam SN Hohmann, Ana C. Rossaneis, Felipe A. Pinho-Ribeiro, and Waldiceu A. Verri. (2016). “Capsaicina: comprensión actual de sus mecanismos y terapia del dolor y otros usos clínicos y preclínicos”. Molecules 21, no. 7: 844. https://doi.org/10.3390/molecules21070844
  • García Torres, C. E. (2020). Macroelementos, elementos traza y metales tóxicos en comidas preparadas para microondas.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.