1. Why is there concern that cell phones may cause cancer or other health problems?There are three main reasons why people are concerned that cell phones (also known as “wireless” or “mobile” telephones) may cause certain types of cancer or other health problems:
   • The number of cell phone users has increased rapidly. As of 2010, there were more than 303 million subscribers to cell phone service in the United States, according to the Cellular Telecommunications and Internet Association. This is an increase from 110 million users in 2000. Globally, the number of cell phone subscriptions is estimated to be 5 billion.
   • Over time, the number of cell phone calls per day, the length of each call, and the duration of use of cell phones have increased and cell phone technology has undergone substantial change. Cell phone use began in Japan in 1979, in Nordic countries in Europe in 1981, and in the United States in 1983, but cell phones were not widely used in the United States until the 1990s.
   • Cell phones emit radiofrequency energy (radio waves), which is a form of non-ionizing radiation. The tissues next to where the phone is held absorb this energy. Potential health effects of radiofrequency exposure from cell phones, radar, satellite stations, microwave ovens, and other sources have been studied for many years. 
2. What is radiofrequency energy, how can it affect the body, and how is it measured in epidemiologic studies?Radiofrequency energy is a form of electromagnetic radiation. Electromagnetic radiation can be divided into two types: ionizing (x-rays, radon, cosmic rays) and non-ionizing (radiofrequency, extremely low-frequency or power frequency). Ionizing radiation, such as that produced by x-ray machines, can pose a cancer risk. There is currently no consistent evidence that non-ionizing radiation emitted by cell phones is associated with cancer risk.When a call is placed from a cell phone, the antenna of the phone sends a signal to the nearest base station antenna. The base station routes the call through a switching center, where the call can be transferred to another cell phone, another base station, or the local land-line telephone system.

   How does radiofrequency energy affect the body? The farther a cell phone is from a base station antenna, the higher the power level needed to maintain a connection. The amount of radiofrequency energy exposure to the user decreases significantly with increasing distances between the phone’s antenna and the user, and, to a lesser extent, shorter distances between the phone and a base station. A cell phone user’s level of exposure depends on several factors, including the following:

   • The number and duration of calls
   • The amount of cell phone traffic at a given time
   • The distance from the nearest base station
   • The quality of the cellular transmission
   • The size of the handset
   • For older phones, how far the antenna is extended
   • Whether or not a hands-free device is used

   The only known biologic effect of radiofrequency energy is heating. A form of this kind of energy is used by microwave ovens. Although high doses of radiofrequency energy cause localized tissue heating, the level of radiofrequency exposure from cell phone use is not sufficient to increase body temperature. There is no consistent evidence that radiofrequency exposure can produce other serious health effects, including cancer. However, more research is needed to determine what effects, if any, this energy has on the body.

   How is radiofrequency energy measured in epidemiologic studies? Two strategies have been used to estimate radiofrequency levels in epidemiologic studies. Radiofrequency levels are estimated by assessing the following information from in-person interviews or self-administered questionnaires:

   • Whether the subject was a “regular” user (minimum number of calls per week/month)
   • The age/year of first use and age/year of last use (duration of use and time since start of use)
   • The average number of cell phone calls per day/week/month (frequency)
   • The average length of a typical cell phone call
   • Total hours of lifetime use, calculated from length of typical call times, number of calls per period, and duration of use 
3. Do cell phones cause cancer? What is the scientific evidence, and what do expert reviewers conclude?There is concern that radiofrequency energy produced by cell phones may affect the brain and other tissues in the head because hand-held cell phones are usually operated close to the head. Researchers have focused on whether radiofrequency energy can cause malignant (cancerous) brain tumors, such as gliomas as well as benign (noncancerous) tumors, such as acoustic neuromas (tumors in the cells of the nerve responsible for hearing), meningiomas (tumors in the meninges, membranes that cover and protect the brain and spinal cord), and parotid gland tumors (tumors in the salivary glands). Researchers have investigated the possible role of cell phones or other sources of radiofrequency exposure and cancer risks in humans and animals. There are also experimental investigations assessing potential biologic or mechanistic effects by which radiofrequency exposure might lead to cancer.Scientific evidence―human studies of cell phone use

   The Interphone Study, a 13-country consortium of case-control studies of cell phone use and risk for malignant or benign brain tumors, is the largest study of long-term cell phone use. Interphone researchers found that cell phone users had reduced risks for glioma and meningioma overall, and they found no evidence of increasing risk with progressively increasing number of calls, longer call time, or years since beginning cell phone use. The small proportion of study participants who reported spending the most total time on cell phone calls (13 percent of people with brain tumors and 8 percent of those without tumors) experienced a statistically significant, albeit modest, increase in risk of glioma.

   There was some indication that the association with glioma among heaviest users of cell phones was more apparent for phone use on the same side of the head as the tumor, but the authors noted that this could have been due to reporting bias. However, if the relationship were causal, it would translate into an increase from the current age-adjusted incidence rate of brain cancer in the United States of about 6.5 cases per 100,000 people to about 9 cases per 100,000. The Interphone researchers considered this finding inconclusive due to implausible levels of use reported by a subset of the heaviest users. Interphone was coordinated by the International Agency for Research on Cancer (IARC).

   Interphone and other case-control studies of acoustic neuroma. The individual studies of cell phone use and risk of acoustic neuroma are based on small numbers of cases. A pooled analysis of data from Interphone investigators from Denmark, Finland, Norway, Sweden, and the United Kingdom did not find relationships between the risk of acoustic neuroma and the duration of cell phone use, cumulative hours of use, or number of calls; however, the risk of a tumor on the same side of the head as the reported phone use was higher among persons who had used a cell phone for 10 years or more. A Swedish case-control study reported similar findings, but a Danish case-control study showed no increased risk in long-term (10 years or more) cell phone users compared with short-term users, and no increase in the incidence of tumors on the side of the head where the phone was usually held. Patients with a tumor on one side of their head might be more likely to report phone use on that side.

   A cohort study in Denmark attempted to avoid some of the biases associated with case-control studies (see below in Question 4) by linking billing information from over 420,000 cell phone subscribers with brain tumor incidence data from the Danish Cancer Registry. Cell phone use was not associated with glioma, meningioma, or acoustic neuroma, even among persons who had been subscribers for 10 or more years. Although this approach does not provide direct data on cell phone frequency or duration of use, and the subscriber may not be the primary user of the phone, the prospective cohort design precludes the need to rely on recall of past cell phone use.

   Most earlier case-control studies in the United States, Europe, and Japan generally did not demonstrate associations of cell phone use with glioma or meningioma, except for case-control studies in areas of Sweden which found statistically significant associations with cumulative use and latency that were highest in subjects with first use before the age of 20. See Question 4 for more information about why these studies may differ.

   Case-control studies of tumors other than brain and central nervous system. There are very few human studies of the possible relationship between cell phone use and tumors other than those of the brain and central nervous system, such as tumors of the parotid gland.

   Cancer trends over time. Incidence data from the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute have shown no increase in the age-adjusted incidence of brain and other nervous system cancers between 1987 and 2007, despite the dramatic increase in the use of cell phones. Similarly, incidence data from Denmark, Finland, Norway, and Sweden for the period 1974-2003 revealed no increase in age-adjusted incidence of brain and other central nervous system tumors. If cell phones play a role in the risk of brain cancer, one might expect to see an increase in rates because average monthly hours of cell phone use have increased regularly for the past two decades in the United States and Nordic countries.

   Scientific evidence―human studies of cancer risks associated with other sources of radiofrequency

   Studies of workers exposed to radiofrequency have shown no evidence of increased risk of brain tumors among U.S. Navy electronics technicians, aviation technicians or fire control technicians, those working in an electromagnetic pulse test program, plastic-ware workers, cellular phone manufacturing workers, or Navy personnel with a high probability of exposure to radar.

   Scientific evidence―animal and mechanistic studies

   Scientists have not yet identified the mechanism by which radiofrequency energy might cause cancer. Exposure to radiofrequency energy does not appear to result in damage to DNA. To date, studies of rodents exposed to radiofrequency radiation provide no clear or consistent evidence that this type of radiation causes cancer, nor that it enhances the carcinogenicity of known chemical carcinogens.

   The National Institute of Environmental Health Sciences, a part of NIH, is carrying out a study of risks related to exposure to radiofrequency radiation (the type used in cell phones) in highly specialized labs that can specify and control sources of radiation and measure their effects on rodents.

   Conclusions of Expert Organizations

   The International Agency for Research on Cancer (IARC), a component of the World Health Organization, has recently classified radiofrequency fields as “possibly carcinogenic to humans,” based on limited evidence from human studies, limited evidence from studies of radiofrequency and carcinogenicity in rodents, and weak mechanistic evidence (from studies of genotoxicity, effects on immune function, gene and protein expression, cell signaling, oxidative stress, and apoptosis, along with studies of the possible effects of radiofrequency energy on the blood-brain barrier).

   The American Cancer Society states that most studies to date have not found an association between cell phone use and development of tumors. However, results from these studies have been limited by the length of follow-up, changing patterns of cell phone usage and technology, lack of study of children, and methods for measuring cell phone use. Possible cancer risks of cell phone exposure should continue to be evaluated using high-quality methodological approaches, particularly in relation to use in childhood and adolescence and longer-term use.

   The National Institute of Environmental Health Sciences (NIEHS) is currently conducting the largest laboratory rodent study to date on radiofrequency energy exposures in rodents; the studies are designed to mimic human exposure and are based on the frequencies and modulations of cell phones currently in use in the United States. NIEHS states that the weight of the current scientific evidence has not conclusively linked cell phones with any adverse health problems, but more research is needed.

   The U.S. Food and Drug Administration, which is responsible for regulating the safety of machines and devices that emit radiation (including cell phones), notes that studies reporting biological changes associated with radiofrequency energy have failed to be replicated and that the majority of human epidemiologic studies have failed to show an association between exposure to radiofrequency from cell phones and health problems.

   The U.S. Centers for Disease Control and Prevention states that although some studies have raised concerns, the scientific research as a whole does not support a significant association between cell phone use and health effects.

   The Federal Communications Commission concludes that there is no scientific evidence to prove that wireless phone usage can lead to cancer or a variety of other health problems, including headaches, dizziness or memory loss. 

4. Why are there inconsistencies among the studies?Even among studies that show an association between cell phone use and cancer, the results are conflicting. Studies in Sweden have reported elevated risks at usage levels where Interphone finds no association. There are several possible reasons for discrepancies between some studies:
   • Information about cell phone use, including the frequency of use and the duration of calls, has largely been assessed through questionnaires. The completeness and accuracy of the data collected during such interviews depend on the memory of the responding individuals. In case-control studies, individuals with brain tumors may remember cell phone use differently from healthy individuals, which can result in a problem known as recall bias.
   • In the Interphone study, cell phone use among people who developed a brain tumor was more likely to be reported on the same side of the head as the brain tumor. Both low users and high users of cell phones reported this pattern, making the predominance of same-side-of-the-head use less likely to be causal; instead, the pattern may reflect over-reporting. Further, there’s no reason to expect reduced risk of tumor occurrence among those using cell phones on the opposite side of the head, as reported in that study.
   • Gliomas are particularly difficult to study in large part because of high mortality and short survival. Patients who survive initial treatment are often impaired, which may affect their responses. Furthermore, for cases who have died, next-of-kin are often less familiar with the cell phone use patterns of the affected family member and may not accurately describe patterns of use to an interviewer.
   • Epidemiologic studies of cell phone use and brain cancer risk lack verifiable data about cumulative exposure over time (the total amount of radiofrequency energy individuals have encountered). These studies are also vulnerable to errors in the reporting of exposure by study participants.
   • Study participation rates are frequently different between those with cancer and those without cancer in brain tumor studies, a problem known as participation bias. Some studies have indicated greater participation by individuals diagnosed with brain tumors compared with control subjects, and participation rates may be related to cell phone use. For example, the Interphone study reported participation rates of 78 percent for meningioma cases (range 56 to 92 percent for the individual studies), 64 percent (range 36 to 92 percent) for the glioma cases, and 53 percent (range 42 to 74 percent) for controls. The Swedish studies reported participation rates of 85 percent in cases and 84 percent in controls.
   • The interval between exposure to a carcinogen and the clinical onset of a tumor may be many years or decades. Memory of events that occurred years to decades ago may be problematic. In case-control studies, it is not possible to prospectively monitor cases and controls for the length of time it might take for brain tumors to develop.
   • Cellular technology continues to change. Although older studies evaluated radiofrequency energy exposure from analog telephones, most cell phones today use digital technology, which operates at a different frequency and a lower power level than analog phones.
   • The use of “hands-free” wireless technology is increasing and may alter exposure.

   Investigators from the Interphone study looked at potential sources of bias that could affect the conclusions of epidemiologic studies. They found lower frequency of regular cell phone use among control subjects than among patients with brain tumors, and they quantified how this difference might affect the study’s results. They found moderate to high correlation between use that was measured (with special software-equipped phones) and recalled use. Light users were more likely to underestimate their use, and heavy users were more likely to overestimate their use and length of calls. A comparison of cell phone subscriber data with reported cell phone use from interviews revealed that both brain tumor patients and control subjects underestimated the number of calls and overestimated call duration. 

5. What studies are still under way that will help further our understanding?A large, prospective cohort study of cell phone use and its possible long-term health effects was launched in Europe in March 2010. This study, known as COSMOS, will enroll approximately 250,000 cell phone users ages 18 or older and will follow them for 20 to 30 years. Participants in COSMOS will complete a questionnaire about their health, lifestyle, and current and past cell phone use. This information will be supplemented with information from health records and cell phone records.The challenge of such an ambitious study is to maintain the cohort over many decades. Researchers will need to determine if those participants who leave the study are somehow different from those who remain throughout the follow-up period.

   Although recall bias is minimized in studies that also link to cell phone records, such studies face other problems. For example, it is impossible to know who is using the cell phone or whether that individual may also place calls using other cell phones. To a lesser extent, it is not clear if multiple users of a single phone are represented on one bill. 

6. Do children have a higher risk of developing cancer due to cell phone use than adults?There are currently no data on cell phone use and risk of cancer in children. None of the published studies to date have included children.  Cell phone use by children and adolescents is increasing rapidly, and they are likely to accumulate many years of exposure during their lives. In addition, children may be at greater risk because their nervous systems are still developing at the time of exposure. A large case-control study of childhood brain cancer in several northern European countries is in progress. Researchers from the Centre for Research in Environmental Epidemiology in Spain are also conducting an international study—Mobi-Kids—to evaluate risk from new communications technologies (including cell phones) and other environmental factors in young people ages 10 to 24. 
7. What can cell phone users do to reduce their exposure to radiofrequency energy?The Food and Drug Administration and the Federal Communications Commission have suggested some steps that cell phone users can take to reduce their exposure:
   • Reserve the use of cell phones for shorter conversations or for times when a conventional phone is not available.
   • Switch to a type of cell phone with a hands-free device that will place more distance between the phone and the head of the user.

   Hands-free kits reduce the amount of radiofrequency energy exposure to the head because the antenna, which is the source of energy, is not placed against the head. 

8. Where can I find more information about radiofrequency energy from my cell phone?The Federal Communications Commission provides information about the specific absorption rate (SAR) of many recent cell phones. The SAR corresponds to the relative amount of radiofrequency energy absorbed into the head of a cell phone user. Consumers can access this information using the phone’s FCC ID number, which is usually located on the case of the phone, and the FCC’s ID search form. 
9. What are other sources of radiofrequency energy?The most common use of radiofrequency energy is for telecommunications. In the United States, cell phones currently operate in a frequency range of about 1,800 to 2,200 megahertz (MHz). In this range, the electromagnetic radiation produced is in the form of non-ionizing radiofrequency energy. Cordless phones (phones that have a base unit connected to the telephone wiring in a house) often operate at radio frequencies similar to those of cell phones; however, since cordless phones have a limited range and require a nearby base, their signals are generally much less powerful than those of cell phones. Among other radiofrequency energy sources, AM/FM radios and VHF/UHF televisions operate at lower radio frequencies than cell phones, whereas sources such as radar, satellite stations, magnetic resonance imaging (MRI) devices, industrial equipment, and microwave ovens operate at somewhat higher radio frequencies. 
10. How common is brain cancer? Has the incidence of brain cancer changed over time?Brain cancer incidence and mortality (death) rates have changed little in the past decade. In the United States, 22,020 new diagnoses and 13,140 deaths from brain cancer were estimated for 2010.The 5-year survival rate for brain cancers diagnosed from 2001 to 2007 was 33.4 percent. This means that 33.4 out of every 100 persons diagnosed with brain cancer today will survive at least 5 years.

    The risk of developing brain cancer increases with age. Between 2000 and 2008, there were fewer than 5 brain cancer cases for every 100,000 people in the United States under age 65, compared with approximately 19 cases for every 100,000 people in the United States who were ages 65 or older.

Selected References 

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