Several national and international agencies study different exposures and substances in the environment to determine if they can cause cancer. (Something that causes cancer or helps cancer grow is called a carcinogen.) The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory and human research studies.
The Specific Absorption Rate test uses sophisticated instruments to measure the amount of radiation absorbed into the body, usually the head. At present, the generally recognized limit for absorbed electromagnetic energy is 1.6 watts per kilogram. All cell phones sold must be tested and have their compliance with this standard certified by their manufacturer. The electromagnetic fields from a cell phone depend upon the design of the cell phone and its antenna,how it operates, as well as how it is held and used. Tests conducted by the ABC show 20/20 has found that some of the country’s most popular cell phones can – depending on how they’re held – exceed the radiation limit. A cell phone’s antenna radiates in all directions. The health concern is about the radiation actually absorbed into the head, which is where cell phones are usually held. SAR tests conducted on the SAR Shield show that the product reduces SAR radiation by as much as 89%.
The most common effect is heat generation (though non-thermal biological harm has also been demonstrated), which can alter the characteristics of various bodily tissues depending on the amount of radiation present and its ability to penetrate the body. Tissue damage can promote the cellular mutations and increase your long-term risk of developing cancer.
If you want to measure the EMF radiation from your own phone, and know if EMF protection products are working, you should get a quality EMF meter. I highly recommend the new TriField TF2 (read my review) as it’s simple to use, lasts forever, is extremely accurate, and measures all three types of EMF radiation. If you’re looking for a low-cost EMF meter I really like the Meterk (read my review).
Radio base licensing procedures have been established in the majority of urban spaces regulated either at municipal/county, provincial/state or national level. Mobile telephone service providers are, in many regions, required to obtain construction licenses, provide certification of antenna emission levels and assure compliance to ICNIRP standards and/or to other environmental legislation.
In addition, the findings might be influenced by the fact that the study subjects owned cell phones that were in some cases manufactured two decades ago. The way we use cell phones and the networks they’re operated on have also changed since then. Last, cancer can develop slowly over decades, yet the studies have analyzed data over only about a five- to 20-year span.
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.