At first glance, the bubbles on my pizza didn’t match my mental image of what a “normal” pizza should look like. They weren’t evenly distributed, and they didn’t resemble the small charred blisters you might see on a wood-fired crust. Instead, they looked inflated—almost like tiny balloons under the cheese.

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Naturally, my brain started throwing out theories:

Air pockets trapped during baking?

Something wrong with the cheese?

A sign of spoilage?

It didn’t help that the internet is full of alarming possibilities when it comes to food safety. But as it turns out, the explanation is far less dramatic—and far more interesting.

The Science Behind the Bubbles
Those strange bubbles are usually the result of a combination of heat, moisture, and the composition of the ingredients—particularly the cheese.

Most commonly, what you’re seeing are pockets of steam and fat forming beneath the surface as the pizza bakes.

Here’s how it happens:

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When pizza is exposed to high heat, several things occur simultaneously. The water content in the dough, sauce, and cheese begins to evaporate, creating steam. At the same time, fats in the cheese start to melt and separate. If the surface layer of cheese melts quickly and forms a kind of seal, that steam can get trapped underneath.

The result? A bubble.

These bubbles can vary in size depending on factors like oven temperature, baking time, and how evenly the ingredients are distributed. In high-heat environments—like pizza ovens or very hot home ovens—this effect becomes even more pronounced.

Why Some Pizzas Bubble More Than Others
Not all pizzas behave the same way, and that’s part of what makes this phenomenon so noticeable when it does happen.

Several variables influence bubble formation:

1. Cheese Type

Different cheeses melt differently. Mozzarella, for example, is known for its smooth melt and stretch, but it can also create surface tension that traps steam. Lower-moisture mozzarella tends to bubble less than fresh mozzarella, which contains more water.

Processed cheeses or blends may behave differently still, sometimes producing more uniform melting and fewer large bubbles.

2. Moisture Content

If your sauce is particularly watery or your toppings release a lot of liquid (think mushrooms or fresh tomatoes), that extra moisture has to go somewhere. As it heats up, it turns into steam—and steam needs an escape route.

If it can’t escape easily, it forms bubbles.

3. Oven Temperature

Higher temperatures accelerate everything: melting, evaporation, and steam formation. That’s why pizzas baked at very high heat—like those in traditional pizza ovens—often develop dramatic bubbling and blistering.

4. Assembly Technique