Using a cleaner in a microwave oven is appropriate if the cleaning product label displays a microwave-safe rating. The owner manual for a particular microwave, usually available from the manufacturer, provides maintenance and cleaning recommendations to prevent product damage.
Microwave oven cleaning has many pitfalls. Chemical cleaners leave residues that can leach into the next meal. Water superheats, causing dangerous splashes. Sponges dry out and catch fire, and pre-soaped cleaning pads leave particles that explode. The key to safe cleaning is following manufacturer instructions and rinsing thoroughly to remove any residual detergent or solution.
To avoid damage, never use oven cleaners, abrasive cleaners or sharp utensils to clean a microwave. Never turn the microwave on while cleaning.