Ask LH: What Should And Shouldn’t I Microwave?

Ask LH: What Should And Shouldn’t I Microwave?
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Dear Lifehacker, I heard it’s dangerous to microwave food in plastic containers or plastic wrap because of scary food-contaminating chemicals. Is that true? What other things are safe or unsafe to use in the microwave? Signed, Nervous Nuking

Pictures: Oleksiy Mark (Shutterstock), State Farm, JoshuaDavisPhotography.

Dear Nervous,

The microwave is a powerful appliance, and with that power comes great potential for harm — things like sparks or explosions and, yes, possible toxins leaching into your foods. But your microwave most likely won’t kill you. Just heed these do’s, don’ts and other recommendations for safe microwave cooking.


What Should and Shouldn't I Microwave?

More often than not, you’re going to need to put your foods and drinks in something to microwave them. Here are the materials that work best as containers and the ones to avoid.


  • Glass containers. These are probably the best to use, since there’s zero debate about how safe they are in the microwave.
  • Most paper plates, towels and napkins. However, because some paper towels are made with plastics and some paper plates and cups are coated with plastic, National Sanitation Foundation (NSF) International recommends only using those products marked as microwave-safe.
  • Ceramics, although Ceramics Today recommends only porcelain and stoneware, rather than ceramic dishes that may have been low-fired, because those could possibly explode; their article offers a test to figure out if a piece would be safe to microwave (if you knock on it and it has a clean ring, it’s probably fine). Plates with metallic paint can also cause sparks.
  • Wax and baking paper, as well as microwave cooking bags are deemed fine too, according to NSF International.


  • Aluminium foil. Technically, you can use foil in the microwave, but it might not be the wisest thing to do.
  • Metal containers, such as canned foods, for the same reason as above.
  • Brown paper bags. Per the USDA: “They are not sanitary, may cause a fire and can emit toxic fumes. Intense heat may cause a bag to ignite, causing a fire in the oven… . The ink, glue, and recycled materials in paper bags can emit toxic fumes when they are exposed to heat. Instead, use purchased oven cooking bags”.
  • One-time storage containers, such as take-away containers, margarine tubs or yoghurt containers
  • Plastic garbage bags, garbage cans or film canisters. I had no idea people consider these cooking vessels, but nevertheless the University of Nebraska warns against using these items for microwave cooking


  • Plastics. This is the big one that people fear might cause cancer. Even BPA-free products leach hormone-like chemicals (although new research suggests it might not be as bad as previously thought). The jury’s still out though on the health implications of microwaving or dishwashing plastics. The Environmental Working Group advises against microwaving foods or drinks in any kind of plastic container at all. Aa Harvard Health reports: “The maximum allowable amount is 100 — 1000 times less per pound of body weight than the amount shown to harm laboratory animals over a lifetime of use. Only containers that pass this test can display a microwave-safe icon, the words ‘microwave safe’, or words to the effect that they’re approved for use in microwave ovens.”
  • Styrofoam. Similarly, some styrofoam products are marked “microwave safe”.
  • If you do decide to microwave in plastic containers, make sure they’re not cracked, old or discoloured. And when covering food with plastic wrap, make sure the plastic doesn’t touch the food.

Foods and Drinks

What Should and Shouldn't I Microwave?

Interestingly enough, even microwaving certain foods can be hazardous to your health or cause accidents, although microwaving food can help certain foods retain more nutrients.



  • Grapes. Apparently they can burst into flame and turn into a glowing ball of plasma gas.
  • Eggs intact in their shells or boiled eggs. The problem, WebMD reports, is the pressure builds up in the sealed egg “container”, which can cause it to explode (even if the boiled egg is peeled). Best to pierce the egg in multiple spots before nuking.
  • Dried hot peppers.’s Chemistry site notes that the capsaicin chemical in peppers is volatile and can catch fire. “Don’t microwave any chemical you wouldn’t want released into the air. Don’t microwave dry materials.”


  • Take care when boiling water in the microwave, because it can be “super-heated” and possibly explode. A chopstick or other stick in the cup would prevent this
  • As with the eggs, cut or prick items that may be more likely to explode because of internal pressure, such as hot dogs, sausages and potatoes. Also make sure you vent any container so steam can escape

Other Objects

You probably already know most metals shouldn’t be put in the microwave unless you want a sparks and lights show. The list of other things you shouldn’t put in the microwave is pretty long, but there are also some unusual, non-destructive ways to use your microwave.


  • Wet sponge to disinfect it. Make sure you squeeze out the dishwashing soap first.
  • Potting soil, to sterilise it, especially good for starting seeds.
  • Dish towels in a zip lock bag for a DIY hot water bottle.
  • DIY heat bag (fill with rice or beans). You can also just fill a sock with these things.
  • Beauty products. Real Simple notes you can briefly warm up products like hot-oil conditioners, hot wax for removing hair, and even facial masks.
  • Water with lemon. It actually cleans your microwave.


  • Dry sponge, which can catch fire.
  • Pretty much anything that’s been done on the Is It a Good Idea to Microwave This? show (videos and wiki here). The microwave specialists tested hundreds of items, including talking greeting cards, firecrackers, spray paint, Pikachu (the doll) and a propane tank. These usually resulted in melting, flames, sparks and smoke.
  • Living things. Enough said.


  • Soap. Well, this is really only debatable if you don’t want to be amazed or waste a bar of soap.
  • CDs. Sometimes you might just want to see a light show or destroy a CD.


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  • … I would be very interested to see paper towels that have plastic in them :/ Cannot imagine what the possible use would be of that.. “Hmm this sure will make them more expensive, toxic and less absorbent what a brilliant plan!” says the Paper Towel Co CEO.

    Also nearly all of these have the addendum of “if not marked microwave safe”. Like you say “One-time storage containers, such as take-away containers,” – but many ARE entirely microwave safe so that you CAN easily reheat and are marked as such…

  • Definitely do not cook eggs in the microwave, that is unless you want to remove all nutritional value from them.

    • I don’t see how it would remove the nutritional value if you don’t overcook it. A recent study showed that steaming vegetables in the microwave was one of the best ways to preserve nutritional value.

      • It’s how the microwave heats the egg whites and yokes that destroys the vitamins. To maintain their vitamins, eggs need to be heated slowly.

        Microwaving does increase the density of the protein in the eggs for all you Atkins dieters.

      • De-natured protein is still protein. In fact in all cooked foods the many of the proteins have been de-natured. Your body is only interested in the constituent Amino acids, it doesn’t care about protein structures.

    • Possibly he means violently….
      Sadly picks up empty shell from microwave.. “Well, there’s just NO nutritional value left in that sucker!”

      …crunch crunch…

  • Every time I boil eggs I must be tempting fate. I’ve always kept them whole, wrapped them in foil and put them in a mug of water and microwaved them. I do this a lot because soft boiled eggs with toast soldiers are the best.

    • If that’s exactly what you do, then the eggs are exposed to microwaves at all – they are heating the water only. You could do the same thinh in a pot of water on a stove and not have to use the foil.

  • for anyone thats curious,
    Microwaving undies is fine, works great and is the best sensation in the world when going to work on a cold winters morning, but it does degrade the elastic rather quick
    but IMHO…. worth it

    • No more than sitting in a hot bath. Microwave energy can heat the testes, but how would they be exposed to the microwaves? There is far too little microwave energy leaking from the oven to cause ANY heating.

    • Be very careful – don’t walk away from the oven while you are doing it or they’ll catch fore if heated too long.

  • Might as well drop it here so people see it- if you want to give some dry bread a new lease on life, wrap it in a damp piece of paper towel and microwave it for 20 seconds. mmm, delicious almost-fresh bread!

  • They’re great for drying tea towels that have got too wet from drying loads of dishes too. 30 seconds should be long enough in most microwaves, any longer and they can dry and catch fire. Don’t ask me how I know :-/

  • I put ants in the microwave once. Nothing happened to them. I admit I may have created a swarm of super ants though.

    • The reason is that the ants arefar smaller than the wavelength of the microwaves and are, in a sense, invisible to them

  • I strongly disagree with your suggestion that beauty products such as wax depilatories and other cosmetics are safe for heating in the microwave oven. This is absolutely NOT true. There have been many injuries as a result of overheated wax from wax depilatories, as well as severe burn injuries from microwave heating pads. I am in a microwave scientist with over 50 years of experience in using microwave ovens and it developed many products based around them, as well as large industrial systems using microwave heating. I do a great deal of expert witness work and know from personal experience that there have been a number of injuries as I’ve cited above. So I suggest you issue a strong disclaimer to avoid the possibility of liability.

    The fact is, that the only things that should be heated in microwave ovens are foods; nonfood products should NEVER be heated in a microwave oven. The reason is primarily because foods contain water and water has a great moderating effect upon how foods heat due to its physical microwave-properties controlling how microwaves interact with water and what happens to the water as it gets hotter. Beauty products contain very little or no water and therefore a very subject overheating.

    I also recommend against heating sponges, cutting boards and dishtowels in microwave ovens. The danger is that if the water evaporates these products contain cellulose which has a peculiar property in microwave exposure in that, when it’s hot, it becomes a very good absorber of microwave energy and subject to catching fire. Again I suggest you issue a disclaimer or you may open yourself up to liability.

    I also recommend against heeding some sponges and cutting boards and dishtowels and microwave ovens. The danger is that if the water evaporates these products contain cellulose which has a peculiar property in microwave exposure in that, when it’s hot, it becomes a very good X absorber of microwave energy and the subject to catching fire. Again I suggest you issue a disclaimer or you may open yourself up to liability.

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