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What Should You Never Put in The Microwave?

Kitchen with wooden cabinets, white background, and black Neff appliances. Food is laid out on the side with a pot on the stove.

The microwave, a staple of the kitchen, and a saviour of our hearts. This convenient little appliance is definitely capable of saving you from dinner disasters, but put the wrong thing in there and you’ll have a whole new disaster on your hands. That’s why we’ve put together a helpful list of things you should never put in the microwave.

Earlier this week, in the Appliance City office, we had a dramatic lunchtime experience. The cause of such drama? A bell pepper.

Collectively, we all have a fairly impressive knowledge of what not to put in a microwave. However, this bell pepper fiasco definitely came as a surprise, and sparked my interest in writing this article (pun intended). 
So what happened? Simply put, a stuffed bell pepper went in the microwave, and a stuffed bell pepper on fire came out. The smell of burnt bell pepper filling the office aside, it was quite a shocking experience. Who knew that bell peppers could cause a microwave fire?! We certainly didn’t! Which got us thinking… What else should you never put in the microwave?

Green bell pepper with stem on fire
(This is not a photo of our bell pepper – that was put out before a photo could be taken and before our boss could see)

Non-Food items you should never put in the microwave


Cutlery drawer full of metal cutlery with wooden spoons to the left.

Metals, even a small amount such as in a metallic paint, should NEVER be put in a microwave. With how dangerous this is, luckily most people already know this. But why exactly is putting metal in the microwave so dangerous?

Microwaves release a type of electromagnetic radiation called (can you guess) microwaves. These waves are absorbed by water molecules found in your food, which in turn heats it up. But, metal cannot absorb these microwaves. This means that electromagnetic energy is built up on the metallic surface. This causes sparks, and in more severe cases, fires or explosions. Metals with thin or jagged edges present an even bigger risk because there is an even bigger build-up of this energy.

Absolutely no metals should be put in the microwave. Here is a list of metallic items that are commonly put in the microwave by mistake:

Aluminium/Tin Foil

Aluminium foil is a really convenient way of wrapping up your food. However, if you place it in the microwave it will very quickly burn and ignite. Not only is this very dangerous for your safety, but it is, obviously, harmful to your microwave.

Dinnerware with metallic trim

White plates with golden metallic trim

Some dinnerware is decorated with a metallic trim. Although this may look very appealing, it does mean that this dinnerware is no longer safe to put in the microwave.

If you’re ever unsure though, you should always check for a “microwave safe” label.

Metal Utensils and Cutlery

Forgetting your fork or spoon on your dish can be such an easy mistake to make. But it is also extremely dangerous. You should never put metal cutlery in the microwave. If you’re lucky, and notice quickly enough, you’ll only cause a few sparks. Otherwise, there is a big risk of fire or explosion.

Insulated Travel Mugs

Close up of person in hot pink jacket holding a travel mug with both hands.

Insulated travel mugs are very often made of steel parts. With this being a metal, it should never meet the inside of your microwave.

Always make sure you check for a “microwave safe” label before taking this risk.

Paper Bags

Paper bags are not equipped to handle the heat of a microwave, and can quickly catch fire. Not only that, but they can also release toxins and fumes when heated up. There are some paper bags that have been designed to be microwave safe; they are made with susceptors that can absorb microwaves. These bags will always be labelled as safe though, so you need to find that label before microwaving.

Cardboard Boxes

Takeaway food in cardboard containers

It’s advisable to avoid microwaving cardboard boxes. In the best case scenario, you put in a plain cardboard box that can withstand a microwave oven for about 60-120 seconds. Past this, it can overheat and catch fire.

Worst case scenario, you put in a cardboard box with a plastic or wax coating that is unable to absorb microwaves.

These coatings can cause sparks and ignite the cardboard, an already highly combustible material.

Single-Use Plastic

When heated, single-use plastic will release the chemicals BPA and phthalates. These chemicals mimic human hormones, and can be extremely harmful. Plastic will also melt into your food, and so you will need to throw your food out if this happens.

There are some microwave safe plastic containers that you can use. These are not single-use, and will always have a “microwave safe” label.


Takeaway food in Styrofoam container

When heated in the microwave, Styrofoam will melt and release similar chemicals into the air and into your food.

There are some polystyrene foam containers that have been created to be microwave safe, but again you will need to look for the label.


If you’re in a rush, it can seem like a good idea to quickly dry your clothes in the microwave. But, simply, it is not. Wet or damp clothes in an electrical appliance can cause an electrical fire. And even if the clothes are completely dry hot spots can form and burn through the material. This can also then lead to a fire. Basically, don’t put your clothes in the microwave. That’s what a tumble dryer is for.

Lidless Containers

This is less of a safety concern, but more of saving you from a big mess. Without a lid on your food, you’re welcoming your food to jump and splash all over your microwave. So unless you fancy an hour or two of cleaning, put a lid on it.


Finally on our list of non-food items that you should never put in your microwave, we come to nothing. This doesn’t mean you shouldn’t put anything in your microwave. We know that’s not true! It just means that you shouldn’t turn it on with nothing inside.

The microwaves need to have somewhere to go, and something to absorb them. If not, they bounce off each other and instead get absorbed by the microwave itself. That’s not a good thing. This means that a microwave can combust, and even explode, with nothing in it.

Nothing can in fact lead to something in the case of a microwave.

Food items you should never put in the microwave

Food is designed to go in the microwave, right? Well, yes, but not all food is created equally. Some foods can spark, explode, or release horrible chemicals when heated in the microwave. If a food can spark, it’s possible that it can catch fire in the microwave. Just like the bell pepper, there were a few food items that we had no idea would be any kind of danger. This was also discovered by Well and Good, when they had their own firework display courtesy of some onions.

Fresh food lined up in modern kitchen

Sparking Foods:

Some foods cause sparks, also known as arcing, when heated in the microwave. This is usually due to foods being high in minerals such as iron, magnesium, and selenium. These minerals act like tiny pieces of metal, causing microwaves to bounce off of them and create sparks. These sparks can sometimes catch fire, such as the case of our bell pepper.

Fresh carrots and onions  bundles together

Foods that cause sparks include:

  • Bell peppers
  • Kale
  • Carrots
  • Onions
  • Green beans
  • Spinach
  • Sliced grapes

Exploding Foods:

A little more dramatic than sparks, some foods explode in the microwave. This is caused by a build-up of steam inside of the food. The steam needs to escape somehow, resulting in an explosion. This usually happens with foods that have a skin or are round. 

Red sauce that has exploded in a white microwave

Foods that can explode include:

  • Boiled or Raw Eggs (Whole)
  • Tomatoes and tomato sauce
  • Potatoes (unless you poke holes in them)
  • Hot dogs (if heated for too long)
  • Whole oranges
  • Spaghetti squash
  • Whole lemons
  • Whole limes
  • Aubergine
  • Whole grapes

Other Dangerous Foods:

There’s only one food in this list, but honestly, it deserves its own list. There is a chance that microwaving hot peppers can cause sparks, similar to the bell pepper. But that’s not the only danger. Heating hot peppers causes it to release capsaicin. This is the chemical that makes them hot. Unfortunately, when released into the air it can get into your eyes and your lungs which is extremely painful. Basically, you may as well just spray yourself with pepper spray.

  • Hot peppers


As much as a kitchen hero that a microwave is, putting the wrong thing in there can be extremely dangerous. From small sparks to big explosions, the damages caused can be brutal. So, if you want to extend the life of your microwave, as well as your own life, make sure that you’re avoiding all of the above mentioned items. Sometimes it’s better to wait a little bit longer and use your stove or oven instead. Stay safe!

If you’re looking for a new microwave, our friendly and knowledgeable sales team would be more than happy to help you. Call us on 0115 965 1937.

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