That brings us back to the main question here: Do cellphones cause tumors? We chose to focus this story on cancer risk, since it seems like the most common health concern people have about cellphones. But before we get to the answers, we need to take another (brief) detour to explain how this science has been done with human subjects. To do that, we need to zoom in on a nerdy subject: research methods.
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.
Transmitters, including cell phones, emit radio signals on more than the assigned frequency. These other signals on other frequencies are “harmonics” and/or “noise” and/or “dirty” signals from less than optimal transmitters, antennae, and/or resonating frequencies emitted from metallic objects in close proximity to the transmitter, like the other components of the cell phone.
Cell-phone designs have changed a lot since the studies described above were completed. For example, the antennas—where most of the radiation from cell phones is emitted—are no longer located outside of phones near the top, closest to your brain when you talk, but are inside the phone, and they can be toward the bottom. As a result, the antenna may not be held against your head when you’re on the phone. That’s important because when it comes to cell-phone radiation, every milli­meter counts: The strength of exposure drops dramatically as the distance from your body increases.
Over time, the number of cell phone calls per day, the length of each call, and the amount of time people use cell phones have increased. Because of changes in cell phone technology and increases in the number of base stations for transmitting wireless signals, the exposure from cell phone use—power output—has changed, mostly lowered, in many regions of the United States (1).