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Things you shouldn't put in a microwave oven

Paper towel, yes. Whole egg, no. Here's how to avoid messy or even dangerous microwave mistakes.

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Last updated: 15 July 2022
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Checked for accuracy by our qualified fact-checkers and verifiers. Find out more about fact-checking at CHOICE.

It's the ultimate in convenient cooking, handy for a wide range of kitchen tasks, not least reheating last night's leftovers. But there are a few things you really should never put in a microwave – either because they're likely to cause a messy explosion or, worse, a serious safety hazard. 

Heed our advice to avoid any microwave mishaps.

1. Aluminium foil and dishes with metal trimming

When sparks fly in the kitchen, you want to hope it's because you're getting romantic with a cooking partner, not because you've accidentally placed a container covered with aluminium foil in the microwave. 

Because, yes, along with dishes that have metallic glazes or trimmings, foil shouldn't generally be used in microwaves, as it can cause sparking and potentially a fire. Small pieces of aluminium foil are usually OK, such as when you're protecting the tips of the wings and legs while defrosting a whole chicken – but foil is still best avoided altogether.

2. Cutlery 

It's easy to forget there's a spoon or fork in the bowl of soup you're heating up, but you should be mindful never to put metal (or plastic) cutlery in the microwave. Anything metal can heat up extremely quickly, which could not only burn you when you take it out, but could also cause sparks that could damage your microwave or cause a fire.

3. Whole eggs

Ever thought, I wonder what would happen if… ? Take our advice – don't try to microwave a whole egg, either raw or cooked. It's perfectly fine to scramble or poach an egg, but never put a whole egg in its shell in the microwave, as the rapid heating (and lack of anywhere for the resulting steam and pressure to escape) will probably cause a messy egg-splosion – see the photo below to appreciate the full horror.

4. Paper bags, plastic packaging and Styrofoam 

Placing paper or cardboard packaging in the microwave is a big no-no, as it can easily catch alight and cause a fire (although CHOICE kitchen expert Fiona Mair advises that paper towel is OK to use for preventing splatters and lining plates when cooking things such as bacon).

Take our advice – don't try to microwave a whole egg, either raw or cooked

You should also be wary of heating anything in plastic packaging or Styrofoam takeaway containers in the microwave. This is because the rapid heating can cause chemicals to leach out through the materials into your food. 

Also, take care when using cling film/plastic wrap – most we've tested are microwave-safe, but some aren't. To be extra cautious, make sure any plastic wrap does not come into contact with your food when microwaving. And always use microwave-safe containers.

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A fine mess: This is what can happen when you reheat a boiled egg in a microwave, as one CHOICE staff member discovered.

5. Anything not labelled 'microwave-safe'

This may seem obvious, but even though you assume it's fine to put anything glass or ceramic in the microwave, they do need to be specifically microwave safe. 

If they're not, they can become dangerously hot when heated and may even crack or melt. Keep in mind that some travel mugs or reusable coffee cups may have stainless steel elements that mean they're not safe to pop in the microwave to heat up your cuppa. 

6. Hot water or your cup of tea

Take care if boiling water or reheating your cold cup of tea in the microwave. Depending on the type of vessel you're using, it can be easy to heat the water beyond boiling point. Not only might this cause a scalding injury when you try to drink it, but the way the liquid is heated can cause it to splatter. 

It's best not to heat excessive amounts of water in the microwave, to follow the manufacturer's instructions precisely, and to take care not to heat it too long.

7. Breastmilk or formula

Because a microwave can heat liquids unevenly, you shouldn't use the microwave to warm breastmilk or formula. Even if you test it, there may be hot spots in the liquid that can easily burn your baby's mouth. 

8. Any foods with a skin and high water content

Any foods that have a skin and a relatively high water content, such as potatoes, tomatoes and citrus fruits, should only be placed whole in the microwave if you have pierced the skin a few times. This will let the steam easily escape when the food is heated to stop it building pressure and exploding, either in the microwave itself or when you bite or cut into it.

9. Nothing

According to Fiona Mair, you should never run your microwave with nothing in it. "The microwaves will have no food or liquid to be absorbed into, so can bounce back into the magnetron and cause damage to the microwave," she says. 

We care about accuracy. See something that's not quite right in this article? Let us know or read more about fact-checking at CHOICE.

Stock images: Getty unless otherwise stated.