Background Information

Cell phones are currently used by 95% of American adults. The U.S. Food and Drug Administration (FDA) nominated radio frequency radiation (RFR) used by cell phones for an NTP study because of widespread public use of cell phones and limited knowledge about potential health effects from long-term exposure.

NTP Studies & Findings

NTP conducted two-year toxicology studies in rats and mice to help clarify potential health hazards, including cancer risk, from exposure to RFR like that used in 2G and 3G cell phones which operate within a range of frequencies from about 700–2700 megahertz (MHz). These were published as Technical Reports in November 2018.

What did the studies find?

NTP uses a standard scale (graphic of NTP’s Level of Evidence Rating System for Cancer Studies) to determine the strength of the evidence for an association between the exposure and findings in the tissues or organs studied. The scale ranges from the highest rating of “clear evidence,” followed by “some evidence,” then “equivocal evidence,” and finally “no evidence.” Different organs or tissues can have different conclusions.

The NTP studies found that high exposure to RFR (900 MHz) used by cell phones was associated with:

• Clear evidence of an association with tumors in the hearts of male rats. The tumors were malignant schwannomas.
• Some evidence of an association with tumors in the brains of male rats. The tumors were malignant gliomas.
• Some evidence of an association with tumors in the adrenal glands of male rats. The tumors were benign, malignant, or complex combined pheochromocytoma.

It was unclear if tumors observed in the studies were caused by exposure to RFR in female rats (900 MHz) and male and female mice (1900MHz).

As a follow-up, NTP published an article in October 2019 that evaluated DNA damage in three regions of the brain, the liver, and in blood cells in rats and mice that were removed at an earlier timepoint from the ongoing 2-year toxicology study. DNA damage, if not repaired, can potentially lead to tumors. This work was also included in NTP’s published Technical Reports, but this study includes analyses of the data in the supporting information not included in the Technical Reports.

NTP scientists found that RFR exposure was associated with an increase in DNA damage. Specifically, they found RFR exposure was linked with significant increases in DNA damage in:

• the frontal cortex of the brain in male mice,
• the blood cells of female mice, and
• the hippocampus of male rats.

There are many factors that influence whether damaged DNA will lead to tumors. NTP plans to conduct additional studies to learn more about how RFR might cause DNA damage. Please see the FAQs below for more information about the specific studies and NTP’s cell phone RFR program.

Are there plans for future studies?

NIEHS scientists in the Division of Translational Toxicology, which supports the National Toxicology Program, undertook research to better understand some of the findings seen in the earlier Radio Frequency Radiation (RFR) rodent studies reported in NTP Technical reports TR-595 and TR-596.

The goals of this new research were to determine the impact of RFR exposure on behavior and stress, conduct real-time physiological monitoring, including evaluation of heart rate, investigate whether RFR exposure induces heating, and evaluate further whether RFR exposure causes DNA damage.

To accomplish these goals:

• Researchers designed and developed a novel custom small-scale RFR exposure system, which included building, testing, and validating the exposure system. This new exposure system was based on the system used in the published NTP rodent studies.
• Researchers then conducted a series of in vivo rodent studies to assess the suitability of the new exposure system. These short-term studies were designed to allow a comparison between the new exposure system and the original exposure system.

NIEHS has completed the feasibility testing of this small-scale RFR exposure system, and the results will be made publicly available and posted on this webpage when internal reviews are finished.

The research using this small-scale RFR exposure system was technically challenging and more resource intensive than expected. In addition, this exposure system was designed to study the frequencies and modulations used in 2G and 3G devices, but is not representative of newer technologies such as 4G/4G-LTE, or 5G (which is still not fully defined). Taking these factors into consideration, no further work with this RFR exposure system will be conducted and NIEHS has no further plans to conduct additional RFR exposure studies at this time.

Complete May 1999

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