Microwave only allow a maximum leak amount of 5mW, which is a really small amount1.
In case some larger radiation is let out, you would experience microwave burns2.
Microwaves radiation is non-ionizing. Differently from x-ray and gamma ray, the microwave photons simply do not have enough energy to cause cancer through ionization3.
Given the previous well-known facts:
- If you are not burned, you are not being affected by microwaves, because they don't leak out.
- If you were to get burned, you would still have no ionizing radiation impact.
Finally, research shows that microwave-length radiation does not cause cancer, but the studies relate mostly to different kinds of microwaves (for example the waves emitted by a cell phone)4.