What is the relationship between cell phones and cancer?

Exposure routes: Radiation that is strong enough to penetrate human tissue

Where found: Electronic devices such as mobile or cellular phones, microwave ovens, and computer monitors that emit radiofrequency radiation

At risk: Possibly people who are exposed to high levels of electromagnetic radiation, such as electric railway workers and those exposed to lower levels of radiation over many years

Etiology and symptoms of associated cancers: Of the dozens of epidemiological studies published since the 1990s on the harmful effects of cell phones, only a few have indicated a possible relationship between cell phone usage and cancer. The overwhelming scientific evidence supports the conclusion that cellular phones do not pose a health risk for the five billion subscribers worldwide. The electromagnetic frequency range of cell phones is from about 850 to 1900 megahertz. Regulatory bodies in the United States do not recognize radiofrequency radiation emitted from a cell phone as a carcinogen, though most state that further research is needed to determine this conclusively; the International Agency for Research on Cancer deemed it a possible carcinogen in 2011.

At high enough levels, radiofrequency energy can damage biological tissue through the application of heat. This energy is essentially what gets produced in a microwave oven when it cooks food. Since mobile or cellular phones emit very low levels of radiofrequency radiation, it had always been assumed that these small electronic devices do not pose a health risk. However, some scientists have argued that long-term exposure to even low intensities of radiation could promote the development and growth of tumors as well as contribute to other kinds of health problems. Because cell phones are placed right against the head, in close proximity to the radiofrequency waves being sent and received, researchers wondered if they would cause damage. Brain tumors, originating from different types of cells, have received the most attention, particularly tumors that have developed on the same side of the head that the individual most often uses when talking on the phone.

The American Cancer Society estimated that 23,380 new cases of brain tumors and spinal tumors would be diagnosed in 2014 in the United States alone. Of these, only a small number of cases can be understood in terms of what has caused the cancer to develop. Unfortunately, little is known about potential mechanisms that might cause brain cancers to develop in general. In terms of cell phone radiation as a possible cause of cancer, no hypothesis has been offered that adequately explains how low levels of radiofrequency energy emitted from cell phones could alter biological tissue or bring harm to the user.

History: The incidence of brain tumors began rising in the 1990s, and this increase cannot be fully explained by the improved diagnostic methods used to detect these tumors. One way to study possible external factors that might be responsible for the increase in tumors is to conduct an epidemiological study. Epidemiological studies look at the frequency of a health problem such as cancer in different groups of people. For example, those who have been diagnosed with a brain tumor are compared with a group who share similar characteristics except they do not have a brain tumor. Scientists can then explore how these two groups might differ in terms of frequency, duration, and exposure intensity of radiofrequency radiation from cell phone usage. One weakness of this type of study is that it is not particularly well suited to determine cause-and-effect relationships.

In 2002, Lennart Hardell from University Hospital, Orebro, Sweden, and his colleagues found an increase in malignant brain tumors associated with the use of analog, digital, and cordless phones. He also found that risks for astrocytomas increased over time and that risk of glioma went up for periods greater than ten years. There did not appear to be an increased risk for meningioma over a long period of time. In another study, Hardell came to the conclusion that there is no association between cell phones and salivary gland tumors. Although Hardell and colleagues have published data that support claims that cell phone use is associated with brain cancer, dozens of other studies have found results to the contrary.

Several studies conducted after 2002 have included much larger numbers of people. Increasing the number of participants can strengthen the research by making it easier for scientists to generalize the results to the overall population. In one of the largest studies on the use of cell phones and risk for cancer ever conducted, more than 420,000 Danish citizens were followed for up to twenty-one years (until 2006). The researchers found no evidence for risk of tumor development from the use of cell phones either in short-term use or in those who had been using cell phones for more than ten years.

A 2008 systematic review in the International Journal of Oncology reported no elevated risk of glioma for long-term users (use for ten or more years), and a 2009 systematic review in the Journal of Clinical Oncology found no association between cell phone use and tumors, including brain tumors, although some studies reviewed indicated an association between use for ten or more years and tumor risk. In 2010 the INTERPHONE international case-control study, conducted in thirteen countries, published its findings in the International Journal of Epidemiology, reporting that cell phone use equal to or exceeding 1,640 hours was associated with higher risk of glioma. However, that and other many studies examining the possible relationship between cell phone use and cancer risk have been limited by participants' recollection of their actual usage.

Overall, the vast majority of research fails to demonstrate that cellular phones pose a threat for cancer development. No relationship has been reliably found when variables such as the number of years used, the cumulative hours of phone use, or the number of calls has been taken into consideration.

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