Radio frequency energy is a form of electromagnetic radiation. Electromagnetic radiation can be categorized into two types: ionizing (e.g., x-rays, radon, and cosmic rays) and non-ionizing (e.g., radio frequency and extremely low frequency, or power frequency). Electromagnetic radiation is defined according to its wavelength and frequency, which is the number of cycles of a wave that pass a reference point per second. Electromagnetic frequencies are described in units called hertz (Hz).

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 radio frequency energy. More information about ionizing radiation can be found on the Radiation page.

The frequency of radio frequency electromagnetic radiation ranges from 30 kilohertz (30 kHz, or 30,000 Hz) to 300 gigahertz (300 GHz, or 300 billion Hz).  Electromagnetic fields in the radio frequency range are used for telecommunications applications, including cell phones, televisions, and radio transmissions. The human body absorbs energy from devices that emit radio frequency electromagnetic radiation. The dose of the absorbed energy is estimated using a measure called the specific absorption rate (SAR), which is expressed in watts per kilogram of body weight.

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 (1).

The only consistently recognized biological effect of radio frequency energy is heating. The ability of microwave ovens to heat food is one example of this effect of radio frequency energy. Radio frequency exposure from cell phone use does cause heating to the area of the body where a cell phone or other device is held (ear, head, etc.). However, it is not sufficient to measurably increase body temperature, and there are no other clearly established effects on the body from radio frequency energy.

It has been suggested that radio frequency energy might affect glucose metabolism, but two small studies that examined brain glucose metabolism after use of a cell phone showed inconsistent results. Whereas one study showed increased glucose metabolism in the region of the brain close to the antenna compared with tissues on the opposite side of the brain, the other study  found reduced glucose metabolism on the side of the brain where the phone was used.

Another study investigated whether exposure to the radio frequency energy from cell phones affects the flow of blood in the brain and found no evidence of such an effect.

The authors of these studies noted that the results are preliminary and that possible health outcomes from changes in glucose metabolism are still unknown. Such inconsistent findings are not uncommon in experimental studies of the biological effects of radio frequency electromagnetic radiation. Some contributing factors include assumptions used to estimate doses, failure to consider temperature effects, and lack of blinding of investigators to exposure status.

Epidemiological studies use information from several sources, including questionnaires and data from cell phone service providers. Direct measurements are not yet possible outside of a laboratory setting. Estimates take into account the following:

• How “regularly” study participants use cell phones (the number of calls per week or month)
• The age and the year when study participants first used a cell phone and the age and the year of last use (allows calculation of the duration of use and time since the start of use)
• The average number of cell phone calls per day, week, or month (frequency)
• The average length of a typical cell phone call
• The total hours of lifetime use, calculated from the length of typical call times, the frequency of use, and the duration of use

Radio frequency 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 National Toxicology Program (NTP), a federal interagency program headquartered at the National Institute of Environmental Health Sciences (NIEHS), which is part of the National Institutes of Health (NIH), recently completed a series of large-scale studies in rodents of exposure to radio frequency energy (the type used in cell phones). This investigation was conducted in highly specialized labs that can specify and control sources of radiation and measure their effects.

In February 2018, two draft technical reports summarizing the findings were made available in advance of the formal peer-review process in March 2018. Peer review is a critical component of the scientific process to ensure that research findings are meaningful, accurate, and appropriately interpreted.

NCI awaits the final peer-reviewed reports from the NTP so that they may be considered for summary inclusion in this fact sheet, along with the existing body of peer-reviewed evidence from human and animal studies. The U.S. Food and DrugAdministration (FDA) issued a statement on the NTP reports stating they “believe the current safety limits for cell phones are acceptable for protecting the public health.” FDA and the Federal Communications Commission share responsibility for regulating cell phone technologies and FDA originally nominated this topic for study by NTP.

Researchers have carried out several types of epidemiological studies in humans to investigate the possibility of a relationship between cell phone use and the risk of 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), most meningiomas (tumors in the meninges, membranes that cover and protect the brain and spinal cord), and parotid gland tumors (tumors in the salivary glands).

In one type of study, called a case-control study, cell phone use is compared between people with these types of tumors and people without them. In another type of study, called a cohort study, a large group of people who do not have cancer at study entry is followed over time and the rate of these tumors in people who did and didn’t use cell phones is compared. Cancer incidence data can also be analyzed over time to see if the rates of cancer changed in large populations during the time that cell phone use increased dramatically. These studies have not shown clear evidence of a relationship between cell phone use and cancer. However, researchers have reported some statistically significant associations for certain subgroups of people.

Three large epidemiological studies have examined the possible association between cell phone use and cancer: Interphone, a case-control study; the Danish Study, a cohort study; and the Million Women Study, another cohort study.

• InterphoneHow the study was done: This is the largest health-related case-control study of cell phone use and the risk of head and neck tumors. It was conducted by a consortium of researchers from 13 countries. The data came from questionnaires that were completed by study participants.What the study showed: Most published analyses from this study have shown no statistically significant increases in brain or central nervous system cancers related to higher amounts of cell phone use. One analysis showed a statistically significant, although modest, increase in the risk of glioma among the small proportion of study participants who spent the most total time on cell phone calls. However, the researchers considered this finding inconclusive because they felt that the amount of use reported by some respondents was unlikely and because the participants who reported lower levels of use appeared to have a slightly reduced risk of brain cancer compared with people who did not use cell phones regularly. Another recent analysis from this study found no relationship between brain tumor locations and regions of the brain that were exposed to the highest level of radio frequency energy from cell phones.