Pong’s research indicates that badly designed cell phone cases can partially block a phone’s antenna, making the device work harder to transmit signals. Due to gaps in the FCC’s cell phone regulations, a phone worn right next to the body and enclosed by a case that obstructs the antenna could expose the user to more radiation than the FCC’s legal limit.
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.
There is no strong or consistent evidence that mobile phone use increases the risk of getting brain cancer or other head tumors. The United States National Cancer Institute points out that "Radiofrequency energy, unlike ionizing radiation, does not cause DNA damage that can lead to cancer. Its only consistently observed biological effect in humans is tissue heating. In animal studies, it has not been found to cause cancer or to enhance the cancer-causing effects of known chemical carcinogens." The majority of human studies have failed to find a link between cell phone use and cancer. In 2011 a World Health Organization working group classified cell phone use as "possibly carcinogenic to humans". The CDC states that no scientific evidence definitively answers whether cell phone use causes cancer.
Manufacturers conduct government-required certification tests using a bare phone, set to transmit at maximum power, with no accessories. The recorded maximum SAR is reported to the FCC and listed in the phone’s manual. A phone tested with accessories under the same conditions can produce a higher SAR because the materials surrounding the antenna can affect the amount of radiation that reaches and is absorbed by the user’s body. A case can influence both the overall amount of emitted radiation and how it is directed.
The Stewart report recommended that children should only use mobile phones in emergencies. The recommendation was based on the theory that children could be more at risk from the radiowaves emitted by mobile phones. This is because their brains are still developing and their skulls are thinner, making it easier for the radiowaves to penetrate them. Also if they start using mobiles at a young age, their cumulative lifetime use will be higher than adults. According to the Advisory Group on Non-Ionising Radiation, “little has been published specifically on childhood exposures” since 2000. As a result, children are still advised only to use mobile phones in emergencies. However, surveys suggest that many children are ignoring the advice. A survey of 1,000 British children, carried out in 2001, found 90% of under-16s own a mobile and one in 10 spends more than 45 minutes a day using it.
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If you're concerned that talking on your cell phone could cook your brain, you may want to invest in an anti-radiation phone case. The basic idea behind these cases is that they redirect the radiation produced by the phone away from the user, so it isn't constantly bombarding your skull. They can accomplish this in a variety of ways; one involves using antennas to redirect the waves, and another uses silicone or other materials to block the waves.
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.