As pizza heats up, moisture trapped in the cheese turns into steam and creates bubbles. High cooking temperatures and the type of cheese used can make this effect even more noticeable.
These bubbles are generally safe to eat and are not a sign that the pizza has spoiled. In most cases, they simply show how the cheese reacted to moisture and heat while baking.
If you want fewer bubbles, you can try lowering the cooking temperature, using a different cheese, or poking small holes in the crust before baking. Otherwise, the bubbly appearance is harmless and the pizza can be enjoyed normally.
