Why do eggs, potatoes and other foods explode when heated in a microwave?

Microwave energy penetrates foods more deeply than during conventional heating. The water molecules inside of the food heats as quickly as those on the outside. When heated, water expands so skinned or shelled foods explode to accommodate the increasing size of the water molecules. To avoid overheating these types of foods, use your microwave's preset cooking feature for more precise cooking times, or reduce the power level during cooking.