Sometimes you've got a bit of leftover pizza and rather than putting it on a plate it would be so much easier to just throw the entire box in the microwave to warm up the pizza in.
But can you microwave a pizza box? Is it safe to do so or will it catch on fire? Also are there any health concerns or chemicals we need to be careful of when microwaving a pizza box.
I often have leftover pizza and while I usually use a plate from time to time I throw the entire box in. So I wanted to run some experiments as well as do some research into whether or not this is safe, and here's what I found.
It's generally safe to microwave a pizza box for a short period of time to warm up some pizza. However, microwaving a pizza box longer than 1 minute can lead to the pizza box catching on fire and recycled cardboard can also contain toxic chemicals which can leech into your food and cause cancer. It's best to simply use a plate where possible.
What Happens When You Microwave a Pizza Box
I wanted to see once and for all what happens when you microwave a pizza box and under what conditions it actually presents a danger and could catch on fire.
When you microwave a pizza inside a pizza box for a short period of time the pizza warms up and no damage is done to the box. But microwaving the box for long enough will cause it to catch on fire.
Below you can see my experiment where I microwaved a pizza box and ultimately ended up setting it on fire way quicker than I thought was possible.
When I put the pizza box in the microwave with pizza in it for 1 minute the pizza got hot and the pizza box was fine.
I personally only had 2 pieces of pizza left in the box and honestly 1 minute was overkill to heat those up, 30-40 seconds probably would have been better.
But then I put the pizza box in the microwave by itself and between 1-2 minutes the pizza box started smoking and smouldering.
I quickly took the pizza box outside and as I held it outside flames erupted out the side of it.
This means the pizza was actually on fire on the inside, I just couldn't see it.
Very quickly the entire box was in flames and I had to put it out with water.
If I had of left it in the microwave or keep it cooking then the fire could have been really bad.
Can You Warm Up Pizza In The Box?
You can warm up pizza in the box in the microwave. The microwaves pass through the cardboard box and are able to heat up the pizza inside.
The cardboard box will absorb some microwaves and get hot itself, but it won't absorb all of them and your pizza will warm up almost as good as if it was on a ceramic plate.
The only time your pizza wouldn't warm up is if the box was completely covered in aluminium foil. The aluminium foil would reflect all the microwaves and none would get to the pizza. But no one is ever going to do that so you don't need to worry about it.
Learn more about if you can microwave aluminium foil (spoiler: you actually can)
So yes, you can warm up pizza in the box but you probably shouldn't do it for longer than a minute unless you want to risk setting the entire pizza box on fire.
Is It Safe To Microwave a Pizza Box? Can It Set On Fire?
Pizza boxes can set on fire in the microwave but there are ways you can more safely microwave pizza boxes and minimize your chances of it bursting into flames.
It only took my pizza box less than 2 minutes to catch on fire!
Microwave in Short Bursts
The cardboard pizza box can heat up to extremely high temperatures in the microwave, this is what ultimately can set it on fire.
However, the cardboard box does not retain heat very well and loses it extremely quickly when you turn the microwave off.
So heating up your pizza in short bursts of 20-30 seconds will decrease your chances of fire.
Each burst you can also check the pizza box for any signs of smoking, smouldering or fires. Meaning you can more quickly fix any problems if they occur.
Don't Microwave an Empty Pizza Box
Putting an empty pizza box in the microwave means that all of the microwave energy is directed into heating up the box itself.
When you heat up a pizza box with pizza in it some of the microwave energy is absorbed by the pizza, meaning your box won't heat up as quickly and is less likely to catch on fire.
Best Way To Warm Up Pizza In The Microwave
Microwaving pizza in the box is NOT the best way to warm up pizza in the microwave.
It does carry a fire danger that can easily be avoided by simply putting your pizza on a ceramic plate and heating up the pizza on that.
You can also add in a glass of water to the side of your pizza. The cup of water apparently helps the base of your pizza to stay crispy while the cheese on top still melts.
You can get really fancy and add a thin strip of alfoil to the bottom of your pizza to try and make it crispy but honestly it's not worthwhile.
If you're going to do that then you may as well heat up your pizza using the fry pan and water method shown in the video below:
Is It Safe To Eat a Pizza If You Cook It On Cardboard?
As I do research into what sort of things you can and can't microwave food in I am quickly discovering that some many different items we are used to heating food in are NOT OK and pose some serious health risks.
In my article on if you can microwave styrofoam I discovered that styrofoam contains trace amounts of styrene which is considered a likely cancer causing carcinogen.
My article on if you can microwave paper also highlighted studies that show that the bleaching process that turns paper white creates toxic chemicals call dioxins which are harmful to humans and are also likely to cause cancer.
But what about pizza boxes? Surely cardboard is safe right?
Sadly, this is not the case.
The BBC put out an article highlighting that recycled cardboard contains toxic mineral oils that can cause all sorts of health problems. These toxic chemicals likely come from newspaper ink that is then recycled into cardboard.
Government scientists in Switzerland found quantities of mineral oils between 10 and 100 times above the agreed limit in foods like pasta, rice and cereals sold in cartons made from recycled cardboard.
An apparently half of cardboard in Europe is recycled cardboard.
This study also showed that paper based food containers (such as pizza boxes) can leach chemicals into your food, especially if it is hot (which pizza usually is).
While I don't know whether or not your pizza box is made from new or recycled cardboard my guess is that it's made from recycled cardboard.
Recycled cardboard is cheaper and most pizza companies would want to save money on something disposable like this. Recycled cardboard is also considered to be better for the environment, which would be another reason why pizza companies would choose it.
So while you can reheat pizza in the pizza box it not only poses a fire hazard if cooked for too long but it also present a toxic chemical hazard. So you probably shouldn't be microwaving your pizza boxes at all.
Would I Personally Microwave a Pizza Box?
Given how quickly my pizza box caught on fire as well as the health hazards associated with recycled cardboard I personally wouldn't microwave pizza in a pizza box anymore.
I used to do it in the past and if I was absolutely stuck and didn't have any plates then I would do it on rare occasions. But where possible I will definitely avoid microwaving pizza boxes moving forward.