US Government Releases Report on Pilot Studies of Cell Phone Radiation and DNA Damage
Safety is not assured and questions remain unanswered.
Electromagnetic Radiation Safety, August 13, 2025
The DTT developed a small-scale radio frequency radiation (RFR) exposure system with a signal generator capable of generating a broader array of RF signals than the 2G/3G signals employed in the NTP studies. This system was developed to allow for efficient testing of later generations of cell phone technology (e.g., 4G and 5G).
To help understand the NTP studies, the DTT conducted 2G/3G pilot studies that were limited to 5 days of exposure and used smaller sample sizes compared to the original NTP studies. Nevertheless, these peer-reviewed studies found statistically-significant (p < .05) (in addition to marginally-significant, p < .10) trend effects of cell phone radiation on DNA damage (Wyde et al., 2025):
"Despite a number of difficulties (i.e., engineering requirements, system modifications, measurement of body temperature during exposure), this small-scale RFR exposure system presents a prototype for investigative toxicological studies by researchers interested in conducting experimental RFR studies in rodent models. High-quality studies to understand the effects of RFR exposure on biological responses are needed given the widespread human exposure to RFR associated with cell phone use."
"Also, NIEHS researchers found that exposure to RFR did not induce DNA damage, after five days of continuous exposure, up to 9 watts/kg in rats and 15 watts/kg in mice." https://ntp.niehs.nih.gov/research/topics/cellphones
And contrary to the report's conclusions, the NIEHS stated:
"The research using this small-scale RFR exposure system was technically challenging and more resource intensive than expected... 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." https://ntp.niehs.nih.gov/research/topics/cellphones
Results of the NTP Studies
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| https://www.niehs.nih.gov/sites/default/files/NTP_cell_phone_factsheet_jan_2024_508.pdf |
Based on the NTP studies, the NIEHS published a peer-reviewed paper which concluded that exposure to radio frequency radiation (RFR) is associated with an increase in DNA damage (Smith-Roe et al., 2020). The NTP found significant increases in DNA damage in the frontal cortex of male mice (both modulations--GSM and CDMA), leukocytes of female mice (CDMA only), and hippocampus of male rats (CDMA only) from 14-19 weeks of exposure to cell phone radiation. Increases in DNA damage judged to be equivocal were observed in several other tissues of rats and mice.
Cell Phone Radiation Follow-up Studies
"NIEHS scientists in the Division of Translational Toxicology, which supports the NTP, undertook research to better understand some of the findings seen in the earlier RFR rodent studies reported in NTP Technical reports TR-595 and TR-596.
They 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 short-term in vivo rodent studies.
NIEHS has completed the follow-up studies with this small-scale RFR exposure system. The results from these follow-up studies are published in a peer-reviewed report posted on the NIEHS website (see sidebar).
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."
RFR Follow-up Studies
"Following publication of the NTP RFR studies, NIEHS scientists conducted additional research to better understand the biological mechanisms that produced tumor development and DNA damage in exposed rodents. Specifically, they set out to understand if the health effects seen in the original studies were due to direct RFR exposure or RFR-induced changes in the temperature of body-tissue.
The scientists designed and developed a RFR exposure system that employed sub-cutaneous chips and implanted temperature data loggers to measure internal body temperature of rodents. Technical advances of the system also supported improved control of the exposure process and testing of 2G, 3G, 4G-LTE, and unmodulated RF signals. The scientists conducted short-term studies using the new system.
The scientists obtained some limited results. For example, scientists observed no changes in rodent behavior during operation of the RFR exposure system. Also, NIEHS researchers found that exposure to RFR did not induce DNA damage, after five days of continuous exposure, up to 9 watts/kg in rats and 15 watts/kg in mice.
Despite these findings, the new RFR exposure system left the body temperature question unanswered. Neither the microchips nor the data loggers successfully measured internal body temperature of the test rodents making it impossible to draw conclusions about the role of tissue heating in RFR-induced toxicity and carcinogenicity. The system is also incapable of testing many of the frequencies associated with newer 5G cell phone technology. It became clear that this experimental approach is insufficient for additional RFR research by NIEHS.
Nevertheless, the study generated useful exposure information that may support further study by other organizations.
The full, peer-reviewed report of the study is published under the title of Development and Testing of a Novel Whole-Body Exposure System for Investigative Studies of Radiofrequency Radiation in Rodents on the NIEHS website."
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Development and testing of a novel whole-body exposure system for
investigative studies of radiofrequency radiation in rodents
Wyde ME, Capstick M, Hall SM, Hooth MJ, Kuster N, Ladbury JM, Roberts
GK, Shipkowski KA, Shockley KS, Smith-Roe SL, Stout MD, Walker NJ. 2025.
Development and testing of a novel whole-body exposure system for
investigative studies of radiofrequency radiation in rodents. Research
Triangle Park, NC: National Institute of Environmental Health Sciences. [https://doi.org/10.22427/
Executive Summary
"The predominant source of human exposure to radiofrequency radiation (RFR) occurs through the use of cell phone handsets. Previous toxicology studies on RFR, conducted in support of the National Toxicology Program (NTP) by researchers at the National Institute of Environmental Health Sciences (NIEHS), found exposure-related effects on body temperature and DNA damage. The studies reported herein were conducted by NIEHS researchers in the Division of Translational Toxicology to better understand the biological mechanisms that produced tumor development and DNA damage in exposed rodents. These studies were not conducted as part of the NTP.
The goals of the current research were to design, construct, and use a small-scale RFR exposure system to conduct toxicological research in rats and mice. One of the primary specific objectives of this research was to test and use new, experimental methods to collect physiological data from animals in real time during RFR exposures, including assessment of body temperature and use of videos for clinical observations. Previously, such data collections were not feasible without cessation of RFR exposure.
A new RFR exposure system based on the technical parameters of the system used in the previous NTP toxicology and carcinogenesis studies was developed for small-scale investigative studies with fewer animals. The system was designed with enhanced capabilities and more flexibility, including the ability to generate additional radiofrequency (RF) signals with frequencies and modulations used in more current wireless communication technologies. After development and installation, the system was rigorously tested and independently verified before animal studies were conducted. Following completion of the mouse study, several system modifications were required before the rat studies could be conducted. These system modifications required significant technical expertise and sometimes took several months to resolve successfully.
A series of 5-day studies was conducted in male or female Sprague Dawley (Hsd:Sprague Dawley® SD®) rats or B6C3F1/N mice to evaluate the effect of exposure to the same Code Division Multiple Access (CDMA)- or Global System for Mobile Communications (GSM)-modulated RF signals used in the previous NTP studies. Video from the cameras in the exposure chambers demonstrated no visible response in either rats or mice at the first time the exposure system was activated, at subsequent system on/off transitions, or during the periods of exposure. Exposure to RFR for 5 days did not induce DNA damage in brain cells (frontal cortex, hippocampus, and cerebellum), or in liver, heart, or blood cells of rats and mice, as measured using the comet assay. These investigative studies of RFR exposure were technically challenging to conduct and, unfortunately, measurement by two different methods did not yield data useful for assessing body temperature during exposure.
Despite a number of difficulties (i.e., engineering requirements, system modifications, measurement of body temperature during exposure), this small-scale RFR exposure system presents a prototype for investigative toxicological studies by researchers interested in conducting experimental RFR studies in rodent models. High-quality studies to understand the effects of RFR exposure on biological responses are needed given the widespread human exposure to RFR associated with cell phone use. The aim of this report is to share knowledge and facilitate advancement in research methodologies for investigating the potential health effects of RFR."
Excerpts
"In the current studies, male rats were exposed to CDMA or GSM-modulated RFR, and female rats and male mice were exposed to CDMA-modulated RFR."
"Based on the homogeneity results of previous analyses that modeled the specific absorption rate (SAR) distribution of RFR across the whole body, rats were exposed at a frequency of 900 MHz, and mice were exposed at 1,900 MHz."
"While reviewing videos captured during exposure (see Section 4.2.3.5), it was noted that the stirrer on the back wall of the control chamber (Chamber 4) did not move throughout the four experiments (male mouse CDMA, male rat CDMA, female rat CDMA, male rat GSM)."
"The signal generator (SMBV-100A, Rhode & Schwarz, Germany) chosen was capable of generating the types of signals used in the previous NTP RFR studies."
"These chambers and the studies described in Section 4.2 utilized a 10-minute on/10-minute off alternating exposure paradigm by which animals in each chamber were exposed for 9 hours and 10 minutes per day over an 18-hour and 20-minute exposure period."
"An RFR field exposure system was designed to enable equivalent exposure conditions to those utilized in the previous NTP 2-year studies and for a smaller number of animals with a smaller facility footprint."
Figure 3: The mouse CDMA study was conducted in July 2020. The rat studies were conducted from September to November 2021.
"During the acclimation period, prior to the start of exposure, it was discovered that the rats were able to chew through the cage filter tops and escape their cage units."
"After system installation, verification, and qualification were completed, a series of four 5-day studies was conducted in Sprague Dawley (Hsd:Sprague Dawley ® SD®) rats or B6C3F1/N mice. The goal of these studies was to further characterize radiofrequency radiation (RFR)-induced changes in body temperature and DNA damage observed in the previous National Toxicology Program (NTP) RFR studies and evaluate the use of new methods for collecting live, real-time data."
"On the first day of the studies, rats were approximately 28–31 weeks (male) or 23 weeks (female) old, and male mice were approximately 33 weeks old. Rats and mice were randomly assigned to one of five exposure groups before the start of the study. Randomization was stratified by body weight that produced similar group mean weights using NTP Provantis software (Instem, Stone, UK)."
"Groups of 10 male and 10 female rats and 10 male mice were housed individually in reverberation chambers and exposed to whole-body RFR via Code Division Multiple Access (CDMA) (Interim Standard 95 [IS-95], 1,900 MHz) or via Global System for Mobile Communications (GSM) single modulation (900 MHz)."
"These studies were conducted under the NIEHS contract with Battelle Memorial Institute (HHSN273201400015C). The studies were initiated at the Battelle testing facility in West Jefferson, Ohio. On May 1, 2021, the testing facility was transferred to a new company, AmplifyBio....For the mouse study, all of the in-life, postmortem, and analytical portions of the study were conducted while Battelle was the testing facility; reporting was conducted under AmplifyBio as the testing facility. The rat studies were conducted under AmplifyBio as the testing facility."
"Body temperature data were unusable because of data quality or data collection issues."
"There were no exposure-related effects on survival or body weights with CDMA-modulated RFR exposure up to 9 W/kg for 5 days in male rats."
"There were no exposure-related effects on body weights with GSM-modulated RFR exposure up to 9 W/kg for 5 days in male rats. On study day 5, body weights showed a negative trend and a significant decrease in the 6 W/kg group compared to the chamber control group."
"Statistical methods were chosen based on distributional assumptions. Unless specifically mentioned, all endpoints were tested for a trend across exposure groups, followed by pairwise tests for each exposed group against the chamber control group. Significance of all trend and pairwise tests is determined by a p value of ≤0.05 and is reported at both 0.05 and 0.01 levels. The room control group was analyzed only by a single pairwise comparison to the chamber control group. The room control analysis was kept separate from that of the other exposed groups and was excluded from all trend tests."
DNA damage from exposure to RFR was assessed in frontal cortex, hippocampus, cerebellum, liver, blood, and heart cell samples from male mice and male and female rats using the comet assay (Table D-1, Table D-2, Table D-3, and Table D-4). For CDMA male mice, there were no significant increases in DNA damage, measured as the percent tail DNA, in cells sampled from the three brain regions, blood, and heart tissue; there was a significant trend test for the percent tail DNA in liver cells that is of uncertain biological significance. For CDMA male and CDMA female rats, no significant increases in the percent tail DNA were observed for any tissue. For GSM male rats, there were no significant increases in DNA damage, measured as the percent tail DNA, in cells sampled from frontal cortex, cerebellum, liver, blood, or heart tissue; there was a significant trend test for the percent tail DNA in hippocampal cells that is of uncertain biological significance.
4.4 Summary: "Five-day studies were conducted in male mice or male or female rats to evaluate the effect of exposure to the same CDMA- or GSM-modulated RF signals used in the previous NTP studies. Video from the cameras in the exposure chambers demonstrated no consistent, exposure-related, and visible changes in activity in either rats or mice the first time the exposure system was activated, at subsequent system on/off transitions, or during the periods of exposure. There were no exposure-related effects on survival or body weights following exposure to RFR for 5 days. There was no increase in DNA damage following exposure to RFR for 5 days, as measured using the comet assay, in brain cells (frontal cortex, hippocampus, and cerebellum), or in liver, heart, or blood cells of mice and rats. Body temperature measurements were collected during the studies using two different devices; however, the data were unusable."
Conclusions
"The studies reported herein were conducted by researchers in the Division of Translational Toxicology (DTT) at the National Institute of Environmental Health Sciences (NIEHS). These studies were not conducted as part of the National Toxicology Program."
"The new small-scale RFR exposure system described in this report was developed by NIEHS/DTT to overcome those limitations with a signal generator capable of generating a broader array of RF signals. In addition to the GSM and CDMA signals at 900 and 1,900 MHz used in the previous NTP studies, the small-scale exposure system could generate signals reflective of more current wireless communications (e.g., Third Generation Partnership Project [3GPP] LTE Frequency Division Duplex [FDD] and Time Division Duplex [TDD], LTE-Advanced, 3GPP FDD/ High-Speed Packet Access [HSPA]/HSPA+, GSM/Enhanced Data rates for GSM Evolution [EDGE]/EDGE Evolution, Time Division-Synchronous CDMA [TD-Whole-body Radiofrequency Radiation SCDMA], Wireless Local-area Network [WLAN]) with frequencies between 9 kHz and 3.2 GHz, modulations with base bandwidths of up to 120 MHz, and carrier frequencies of up to 3,200 MHz."
"In these studies, evaluation of video from the cameras in the exposure chambers demonstrated no consistent, exposure-related, and visible changes in activity in either rats or mice the first time the system was activated, during subsequent system on/off transitions, or during the periods of exposure."
"Equivocal results, showing limited statistically significant effects, were observed for male mouse liver cells (CDMA) and male rat hippocampal cells (GSM) in these 5-day studies. Although it is not possible to directly compare the 5-day and 90-day comet assay studies, it is interesting to note that a positive result for hippocampal cells from male rats exposed to CDMA was observed in the 90-day study."
"High-quality studies to understand the effects of RFR exposure on biological responses are needed given the widespread human exposure to RFR associated with cell phone use."
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Open access report: https://www.niehs.nih.
https://www.niehs.nih.gov/
