Putting aluminum foil in the microwave is dangerous. Metals in general are not microwave-safe because they can cause fires. To protect yourself from fire hazards and avoid damaging your microwave, only microwave foods in microwave-safe containers, such as glass or ceramic bowls or plastic containers specifically labeled for microwave use. However, depending on the manufacturer's recommendations, it can be safe to use very small amounts of aluminum foil in the microwave if you take special care.
How Microwaves Work
Microwaves heat food quickly by converting power from an electrical socket into electromagnetic waves. When these waves pass through food, they cause sugars, fats and water molecules to vibrate. The fast vibrations raise the temperature of the food, just like your hands become warm when you rub them together very quickly. It's a popular myth that microwaves cook food from the inside out, but this isn't true. Microwaves can only penetrate through about 1 to 1½ inches of food.
Metal in the Microwave
The problem with metal in the microwave is that it doesn't absorb microwaves like water, sugars and fats do. Therefore, the practical reason why you shouldn't microwave food wrapped in aluminum foil or in metal containers is that the food will not get hot, since the microwaves cannot penetrate through the foil or the metal container. Metal reflects microwaves, similar to the way a mirror reflects light. The microwaves reflecting back onto the parts of your microwave oven, rather than being absorbed by food, can damage the microwave oven's working parts.
A particular problem with aluminum foil in the microwave has to do with its texture. Aluminum foil is easily wrinkled and has sharp edges and corners. The microwaves reflecting off the aluminum foil can cause sparks and arcs of electricity between two points of the metal as the air around the foil becomes electrically charged. This is a serious fire hazard and can damage your microwave oven.
Using Aluminum Foil Safely
According to the USDA Food Safety and Inspection Service, it's possible to use aluminum foil safely in a microwave oven. Because microwaves don't penetrate foil, it's useful for covering parts of food that could get overheated, such as chicken wing tips. If you use aluminum foil in the microwave, only use new, uncrumpled foil; cover less than one-fourth of the food with foil; don't let any edges stick out; keep the foil more than one inch away from the walls of the microwave; and immediately stop the microwave if you see sparks. Read the owner's manual before you put aluminum foil in the microwave to make sure it's okay with your model.
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