In this frequency range, the interaction between matter and light is via the electric field component of light (totally different from how ionizing radiation messes you up). In particular, an oscillating electric field causes polar molecules to rotate or attempt to rotate, and the lag between the applied field and the response of the molecules manifests as dissipation—i.e. heating . This is the same dielectric heating which is the operating principle behind microwave ovens (which operate at 2450 MHz  similar to wifi). So if cell phones were to cause damage to tissue, the mechanism would be the same as what happens in a microwave oven—boiling the water in your head/body.
Several nations have advised moderate use of mobile phones for children. A journal by Gandhi et al. in 2006 states that children receive higher levels of Specific Absorption Rate (SAR). When 5- and 10-year olds are compared to adults, they receive about 153% higher SAR levels. Also, with the permittivity of the brain decreasing as one gets older and the higher relative volume of the exposed growing brain in children, radiation penetrates far beyond the mid-brain.
Because of inconsistent findings from epidemiologic studies in humans and the lack of clear data from previous experimental studies in animals, in 1999 the Food and Drug Administration nominated radiofrequency radiation exposure associated with cell phone exposures for study in animal models by the U.S. National Toxicology Program (NTP), an interagency program that coordinates toxicology research and testing across the U.S. Department of Health and Human Services and is headquartered at the National Institute of Environmental Health Sciences, part of NIH.
The guidelines created a measure of the rate that body tissue absorbs radiation during cell phone use called the specific absorption rate (SAR). The SAR for cell phone radiation was set at a maximum of 1.6 watts of energy absorbed per kilogram of body weight. The limit was set due to the thermal effects of cell phone radiation (all RF radiation can heat human body tissue at high enough levels) - it was not set to mitigate other biological effects cell phone radiation might have such as DNA damage or cancer.
I have not gotten a cell phone, I was gifted a tablet, but it stays off most of the time, I use a desktop PC and my home phone is still landline but cordless. For me it’s been a bit of mixed bag in that I don’t want to rely so heavily on technology to do and remember things for me. When I hear about the new and latest tech that can now do X,Y, or Z for you, I think of the two little boys in the 80’s Cafe in BTTF.
Rats were exposed to radiation with a frequency of 900 megahertz, typical of the cellphones in use when the study was conceived in the 90s, for about nine hours per day for two years, The New York Times reports. The lowest levels of radiation used in the study were equivalent to the maximum exposure a phone can cause and still receive federal regulatory approval; the highest levels to which the animals were exposed were four times that.
We really do not recommend any kind of chip, guard, anti-radiation "filters" or incomplete shielding case because honestly, how could they NOT provide a false sense of security? Folks could believe these products make them “invincible” against radiation so they are comfortable holding the case right up to their heads-and the radiation seeping from the back and the side of the phone case is in very close proximity to their precious brains. Oh no!
Some products (http://www.safecell.net/reports01.html for example) are tested using a piece of shielding material in a laboratory test jig. These tests legitimately show the amount of radiation which penetrates the shield, but results will be very different when compared to putting a small amount of the same shield on a large transmitter like a cellphone. Remember, the entire phone radiates. Placing a small amount of shielding, even if it is an effective shielding material, only shields that small area at best. Think about this analogy: no light will penetrate a penny as it is a very effective light shield, but it is silly to think that holding a penny up to the sun will put you in darkness.
The research continued, and what it uncovered would be a dire warning to cell phone users and the industry’s worst nightmare. When the findings were ready for release in 1998, the scientists were suddenly confronted with another challenge: the industry wanted to take over public dissemination of the information, and it tried everything it could to do so. It was faced with disaster and had a lot to lose.
I love this case. However, I don't understand what happens to the radiation that must collect under the case; isn't there a burst of radiation when the case is opened? I posted this question but the answers were from people who hadn't thought of that issue; they didn't have the answer, except for one who theorized that the radiation is slowly leaking out the top, bottom, and sides. I assume the case keeps radiation off the hand that holds the case with the phone in it, which is great, but I do wonder about the stored radiation when, for example, I'm listening to a podcast with the case closed, then open it later.
Our recommendation is to reduce your exposure from wireless sources. We advocate what’s referred to as the Precautionary Principle. Basically, this means that because there’s research, lots of it actually, saying the energy that powers our cellphones (RF radiation) could be causing health concerns like tumors and cancer. We ought to take care when using our cell phones and all devices that emit RF, using them mindfully.
The energy of electromagnetic radiation is determined by its frequency; ionizing radiation is high frequency, and therefore high energy, whereas non-ionizing radiation is low frequency, and therefore low energy. The NCI fact sheet Electromagnetic Fields and Cancer lists sources of radiofrequency radiation. More information about ionizing radiation can be found on the Radiation page.