Why Do Some Mugs Get Hot In The Microwave? (Explained)

Categorized as Microwave Safety
Why Do Some Mugs Get Hot In The Microwave?

Do you ever put a mug of coffee or tea in the microwave, and it gets too hot to hold? And we’re not just talking about lukewarm – we’re talking scalding hot.

So why does this happen? And more importantly, is there anything you can do to prevent it? Let’s take a look.

Here is The Answer To Why My Mug Gets Hot In The Microwave:

The most common explanation why some mugs get hot in the microwave is because of improperly formulated glaze on the ceramic material.

Some mugs made by some manufacturers from other countries, don’t follow the proper guidelines for glaze formulation and end up with glasses containing lead or other metals that cause the mug to get so hot.

This is not to say that all mugs made in other countries contain heavy metal. There are still a lot of other manufacturers that make their mugs following the proper guidelines.

I don’t know why this happens. Maybe some manufacturers try to decorate their mugs by using glazes with these metals without knowing the potential dangers, or perhaps they just don’t know the proper glaze formulations.

Whatever the reason is, you have to be careful what mug you buy and always make sure to test your mugs first before microwaving them, even if the mug has a “microwave safe” logo on it.

Another reason why some mugs get hot when microwaved is that there is water entering the porous material of the mug.

In essence, a microwave works by heating polar molecules in water or other substances such as fats, oils, sugar, and salt. Without the presence of water, a mug should not get as hot inside a microwave.

But how does water enter a porous material? Well, there must be some tiny cracks or openings in the glaze due to wear and tear that allows water to enter the porous material underneath.

Every time you use your mug or run it through the dishwasher, you are causing the water to seep in the mug more and more.

Eventually, this can accumulate moisture inside the porous material so much that it becomes very easy for your mug to get hot in the microwave.

Do you think it is time for you to change your mug? If you think so, consider getting one made from glass or china (porcelain) because these materials do not absorb water as much as stoneware.

How To Tell If a Mug is Microwave Safe

Keep in mind, even if the microwave-safe label is not 100% accurate, you’ll still want to buy a mug with a microwave-safe label on it or a clear indication that the mug is either microwave-safe or not.

As mentioned previously, if you’ve just recently bought new tea or coffee mug or you’re unsure if your older mug is safe to use in the microwave, you’ll want to test it to make sure it’s truly microwave safe.

Here’s how:

1. Fill a Glass Cup With Water

The first thing you want to do is fill a glass cup with water three-quarters full, then put it side by side to the mug you wish to test.

One thing that you need to remember is the cup that you use to fill up with water must be microwave-safe; otherwise, the test won’t be accurate.

Normally, a glass cup is safe to use in the microwave but to be sure; you can always check the glass for a microwave-safe stamp or words on the bottom.

2. Set Your Microwave To The Highest Power

After that, you want to set your microwave oven to its highest level of power. The method varies between microwaves, so you may want to refer to your owner’s manual for instructions on how to do this.

Generally, for most microwaves, you will find a “power,” “power level,” “menu,” or “settings” button on the keypad. The default setting is usually “100%” or the highest power.

3. Heat Your Mug and Glass Cup Simultaneously

Microwave your mug and cup for 1 minute. Once the time is up, use oven mitts to take out both the cup and mug, then place your hand on the mug to feel how hot it is.

If the mug is warm, it is not safe to use in the microwave. A warm mug indicates that the mug absorbs heat. On the other hand, if the mug is cool, but the glass cup is hot, the mug is microwave safe.

What Happens If You Microwave a Non-Microwavable Mug?

The main reason non-microwaveable mugs or dishes are labeled as such is because they absorb energy and cause the mug to get hot enough to burn your hand when you touch it.

Depending on the materials that are used to make the mug, it can become extremely hot to the point it is shattered. Other materials such as plastic or foam mugs are more likely to melt from the thermal stress that happens.

Lastly, let’s not exclude the possibility that some mugs may contain metal which can cause electric arcs when it comes in contact with high-frequency electromagnetic fields inside a microwave oven.

That said, you don’t need to throw away your mug if you’ve accidentally microwaved it, it should be just fine to use as long as the piece hasn’t completely shattered or turned into a melted blob.


1. Can You Microwave a Mug With a Cork Bottom?

Microwaving a mug with a cork bottom is not recommended. It comes with fire and toxic fume risks that cannot be fully eliminated. Safer options are separate liquid heating, mug warmers, immersion methods, or using mugs with ceramic, glass, or silicone bottoms.

Final Thoughts

There are several reasons why some mugs get hot in the microwave. The most common explanation is that the mug contains small or large amounts of metal that cause it to heat up quickly.

Another reason is that water can enter the porous material of the mug, eventually accumulating so much inside that it becomes easy for the mug to get hot in the microwave.

To be sure whether a mug is microwave safe, the best thing to do is to test it by filling a glass cup with water and putting it together with the mug you want to test in the microwave.

By Rosie Elliott

I’m Rosie. I’m a professional chef with experience in Western, Mediterranean, and Italian cuisine. I’ve been cooking for over 15 years, and I have two daughters that keep me busy!