Does the inside of your microwave look gross? A pretty good solution which I read in a magazine a few years ago (can’t recall the mag) explained how using vinegar, water and lemon juice would naturally clean the inside of the microwave.
The solution:
combine 1/2 cup of water and 1/2 cup of white vinegar in a bowl and squirt in some bottled lemon juice.
Microwave on 50% power for 8 minutes, leave the door shut and let the solution work for 5 or so minutes AFTER the timer goes off.
You should be able to wipe down the inside with a paper towel and all the grime will come off. Of course if you microwave hasn’t been cleaned in a long time then good old elbow grease might be the only solution.