If you stand in front of the microwave while it's on, many people say it won't be that harmful to you if the door is latched. But of course most of us don't like to take chances with our health. Microwaves are a fairly low frequency form of radiation and that means their affect on the body, if any, would be less dangerous than higher frequency forms. Still, many people argue that this radiation can affect us, even though microwave doors are designed to keep it in.
Microwaves could leak out from the spaces in the oven near the door. It's very important to keep the microwave oven clean as dirty ovens are more likely to leak than clean ones. The door must absolutely latch and create a seal when closed. Never use a microwave with a faulty door.
The United States Food and Drug Administration (USFDA) has regulations for maximum radiation levels that microwave oven manufacturers must follow. The lining material in the door also helps keep in harmful microwaves. When these ovens were being invented and tested, early researchers damaged their kidneys because they would stand in front of ones without doors or with the doors open. Small amounts of microwaves can still leak through the cracks in the door opening, so these could reach you if you stand in front of the oven while it is on.
Some people note that even if the amount of radiation is small, it is harmful to stand in front of the microwave while it is cooking food. Studies have been unable to prove this conclusively. The amount of radiation emitted by cell phones is higher than that produced by a microwave oven and some researchers noted that continued cell phone use could lead to cancer, while nothing conclusive has been found.
The radiation emitted by x-rays and gamma rays is called ionized radiation, while that produced by microwaves as well as radio waves is non-ionized radiation. The difference between ionized and non-ionized radiation is that they have different frequencies, or the amount of vibrations they produce each second. The higher frequency, or ionized, radiation has been show to cause cancer in some cases. Microwave ovens use a low frequency, or non-ionized, form of radiation but there is still much controversy as to whether it is completely safe to stand in front of one while it's on.