There have been allegations of radiation injury from microwave ovens. But the injuries ever reported or documented have been injuries that could have happened with any oven or cooking surface. For example, the hot food, splattering grease, or steam from food cooked in a microwave oven has burned people.
We know that the metal walls of the microwave and the wire meshing on its door reflect all the microwaves and stop any of them from escaping the cooking chamber. On the other hand you must have observed that sound waves can easily travel through these walls (the sound of popping popcorn even though slightly muffled is clearly audible even from a distance). The fact is that these two types of waves are very different and the chamber's walls handle them very differently. Any type of wave will partially reflect from a surface if passing through that surface causes the wave's speed to change. Since both sound waves and microwaves change speed when they encounter the cooking chamber's metal walls, they both partially reflect. The sound that you hear when popcorn pops inside the oven is slightly muffled because the sound is having some trouble escaping from the cooking chamber. However, the speed change for the microwaves is so enormous that the reflection is complete. No microwaves at all escape from the cooking chamber! You can think of this in the following terms. Hold up a mirror in front of your face, you can hear what is happening on the other side but can’t see anything as the light waves are reflected completely by the mirror’s reflecting surface.
We are continuously being bombarded by microwaves from natural as well as man made sources. Even our own bodies emit microwaves. The reflective capabilities of metal walls is used in experiments that are sensitive to microwaves. These experiments are performed inside "Faraday cages". A Faraday cage is a metal or metal screen box. Its walls conduct electricity and act as mirrors for electromagnetic waves. As long as a wave has a wavelength significantly longer than the largest hole in the walls, that wave will be reflected and will not enter the box. Because conducting surfaces reflect electromagnetic waves, you can shield a room from electromagnetic waves by enclosing it in conducting surfaces.
There are concerns that microwaves may interfere with the functioning of pacemakers. If a microwave oven doesn't leak microwaves, then it won't affect such people at all. However, if microwaves do leak from a particular microwave oven, they will cause undesirable currents to flow in the electric leads of the pacemaker. There are many other microwave using products that could have the same effects, mobile phones being a prime example. This problem has largely been resolved since pacemakers are now shielded against all electrical interference.
