How often should a microwave oven be cleaned?

Wipe spills and spatters with a water-dampened paper towel as soon as they occur. Stubborn stains may be scrubbed away with a mild solution of dish soap and warm water, says the U.S.D.A. Food Safety & Inspection Service.

Clean small spills from the inside of a microwave oven after every use. Remove stuck-on food residue with steam. Fill a microwave-safe glass bowl with water, add lemon juice or baking soda, and bring to the boiling point. Allow the mixture to cool inside the oven without opening the door. When the water stops steaming, wipe the inside of the oven with a soft cloth or paper towel. To prevent electrical shock, unplug the oven before cleaning.