Direct microwave exposure
Direct microwave exposure is not generally possible, as microwaves emitted by the source in a microwave oven are confined in the oven by the material out of which the oven is constructed. Furthermore, ovens are equipped with redundant safety interlocks, which remove power from the magnetron if the door is opened. This safety mechanism is required by United States federal regulations.
[60] Tests have shown confinement of the microwaves in commercially available ovens to be so nearly universal as to make routine testing unnecessary.
[61] According to the
United States Food and Drug Administration's Center for Devices and Radiological Health, a U.S. Federal Standard limits the amount of microwaves that can leak from an oven throughout its lifetime to 5 milliwatts of microwave radiation per square centimeter at approximately 5 cm (2 in) from the surface of the oven.
[62] This is far below the exposure level currently considered to be harmful to human health.
[63]
The radiation produced by a microwave oven is non-ionizing. It therefore does not have the cancer risks associated with
ionizing radiation such as
X-rays and
high-energy particles. Long-term
rodent studies to assess cancer risk have so far failed to identify any carcinogenicity from 2.45 GHz microwave radiation even with chronic exposure levels (i.e. large fraction of life span) far larger than humans are likely to encounter from any leaking ovens.
[64][65] However, with the oven door open, the radiation may cause damage by heating. Every microwave oven sold has a protective
interlock so that it cannot be run when the door is open or improperly latched.
Microwaves generated in microwave ovens cease to exist once the electrical power is turned off. They do not remain in the food when the power is turned off, any more than light from an electric lamp remains in the walls and furnishings of a room when the lamp is turned off. They do not make the food or the oven radioactive. Compared to conventional cooking, the nutritional content of some foods may be altered differently, but generally in a positive way by preserving more micronutrients -
see above. There is no indication of detrimental health issues associated with microwaved food.
[66]
There are, however, a few cases where people have been exposed to direct microwave radiation, either from appliance malfunction or deliberate action.
[67][68] The general effect of this exposure will be physical burns to the body, as human tissue, particularly the outer fat and muscle layers, has similar composition to some foods that are typically cooked in microwave ovens and so experiences similar dielectric heating effects when exposed to microwave electromagnetic radiation.