Boiled eggs can explode in the microwave due to a build-up of steam pressure inside the egg. When you boil an egg, the water inside the shell turns into steam, and this steam is trapped within the egg. As the egg heats up in the microwave, the steam pressure can build up to the point where the eggshell cannot contain it anymore. As a result, the egg can explode, making a mess in your microwave.
The key reason for this is that the eggshell is impermeable to air, but steam can still pass through it. When the steam inside the egg cannot escape quickly enough, it causes the pressure to rise until the eggshell cracks or explodes.
To avoid this problem, it's essential to never microwave a whole egg with the shell intact. Instead, if you want to reheat a hard-boiled egg or cook it in the microwave, it's best to remove the shell first. You can either slice the egg into smaller pieces or use a microwave-safe container to heat it.
Here's a safer way to reheat a hard-boiled egg in the microwave:
Peel the boiled egg and cut it into smaller pieces if desired.
Place the egg pieces in a microwave-safe container.
Cover the container with a microwave-safe lid or microwave-safe plastic wrap with a small vent hole to allow steam to escape.
Heat the egg pieces in short intervals at medium power, checking and stirring them after each interval to ensure even heating.
By following these steps, you can avoid steam pressure build-up and prevent the eggs from exploding in the microwave.