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Microwave radiation dangers depend on the length of time exposed, the distance from the source, and the power level of the emitting device. Calculating the dangers of microwave radiation depends significantly on where it falls on the radiation spectrum, from high frequency waves such as gamma rays near the top of this list, to low frequency waves like radio waves near the bottom. Microwave frequencies are slightly more energetic than radio waves, whereas the radiation of televisions and computer screens falls immediately below that of radio waves and is classified as extremely low frequency (ELF) radiation. Ionizing radiation is also much more dangerous than non-ionizing radiation, as it has the potential to damage the DNA in human cells. High energy gamma rays, x-rays, and some ultraviolet radiation are ionizing, but not microwaves.
The power of microwave oven radiation in fact is less energetic than that of ordinary visible light. That's not to say that microwave radiation doesn't pose any risks at all, because exposure to it can be quite common. Not only do ovens emit microwave radiation, but cellular phones do also.
For microwave ovens specifically, the main danger posed is one of proximity. A standard microwave oven emits about 600-700 watts of power to cook food. Under United States federal guidelines, the maximum allowed leakage of radiation from a microwave oven in use is 5 milliwatts, which is 0.005 watts per square centimeter (5 mW/cm2). This radiation leakage also drops off by a factor of 10 with a square of the distance from the source. If someone were receiving 5 milliwatts of exposure by being one inch (2.5 centimeters) from the microwave oven as it operated, stepping back a distance of 10 inches (25.4 centimeters) would reduce this exposure by a factor of 100, or to 0.00005 watts.
By contrast, a cellular phone's microwave radiation level is about one milliwatt per centimeter squared (1 mW/cm2). The microwave transmission towers for cell phone signals are typically in the range of 300 watts. Typical microwave power levels in houses close in proximity to cell phone towers have been shown to be one million times below the limits established by the International Radiation Protection Association (IRPA).
Holding a cell phone and its receiving antenna slightly away from the head, encasing it in a carrying pouch, or using ear phones so that the device could be set down at a distance will reduce exposure to microwave radiation to a great degree. Nevertheless, ongoing studies as to potential dangers cell phones pose, especially where used by growing children, continue. Radar detectors used by police officers in patrol cars also generate microwaves, and these units are being studied to determine if there is any long-term risk of exposure, but so far the evidence has not shown any adverse effects. Despite this news, studies in Russia have demonstrated that long-term exposure to very low levels of microwave radiation can pose health risks, and this has led to Russian and European Union safe limits of 1 mW/cm2 versus the established safe limit in the U.S. of 5 mW/cm2.
Probably the greatest danger of microwave radiation as of 2011 is the potential risks of what it does to certain food molecules when cooked. It has been shown that microwave cooking can denature proteins, vitamins, and minerals by breaking them up into smaller molecules that have little nutritional value. The cooking process can also create radiolytic compounds, chemicals decomposed by the effects of radiation that may pose some health risks, such as being carcinogenic, reducing immune function, or impairing memory. Due to these unknowns, baby formula and blood for transfusions is never heated by microwave radiation in hospitals. It is also known that certain soft plastic food packaging has the potential to leach plastic compounds into food if it is used as a container or covering in the microwave, and it is therefore recommend that food be microwaved only in glass or plastics clearly designated as microwave-safe.