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.
A few epidemiology studies have reported higher rates of tumors inside the skull among people who use cell phones heavily for 10 years or more. Of particular concern are benign Schwann cell tumors called acoustic neuromas, which affect nerve cells connecting the inner ear with structures inside the brain. These growths can in some instances progress to malignant cancer with time. But other studies have found no evidence of acoustic neuromas or brain tumors in heavy cell phone users.
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
But this study also has some drawbacks. First, it is based only on whether or not people had a cell phone subscription at the time. It didn’t measure how often these people used their phones (if at all), or if people who didn’t have a subscription used someone else’s phone. There are also limits as to how well this study might apply to people using cell phones today. For example, while the cell phones used at the time of the study tended to require more power than modern cell phones, people also probably used the phones quite a bit less than people use their phones today.

Exposure to ionizing radiation, such as from x-rays, is known to increase the risk of cancer. However, although many studies have examined the potential health effects of non-ionizing radiation from radar, microwave ovens, cell phones, and other sources, there is currently no consistent evidence that non-ionizing radiation increases cancer risk in humans (2).