Take a closer look at the product claims. Many refer to their “shielding technology” and not the product itself. In many cases, the “FCC Certified” labs they cite are actually testing how much RF the raw shielding material can block. They’re testing the materials used in the products. They’re not testing how much RF the actual products block while on a real-world phone.
Current regulatory standards (SAR Test) only protect us from thermal or heating risks; yet, many hundreds of laboratory studies have found that low-intensity, non-thermal exposure to cell phone radiation can promote carcinogenic mechanisms. Moreover, research on humans has found that 25 years of mobile phone use is associated with a three-fold risk of brain cancer. –Joel M. Moskowitz, Ph.D. School of Public Health. University of California, Berkeley
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.