Ever since mobile phones came along, even before they were “smartphones”, people worried that the signal was causing health problems. Studies generally showed them to be perfectly safe, but a bombshell report released in 2018 by the U.S. National Toxicology Program sparked new concerns.
Do phones actually raise a risk? A new international study suggests that the answer is a resounding ‘no’.
In a coordinated experiment that stretched across borders and rat lifetimes, researchers in South Korea and Japan found no meaningful link between long-term exposure to mobile phone radiofrequency (RF) signals and tumors in the brain, heart, or adrenal glands.
Revisiting the Argument
The findings of the 2018 report shook things up, and this wasn’t the only concerning study. RF radiation has been classified as “possibly carcinogenic” since a 2011 review by the International Agency for Research on Cancer. Later studies, including the NTP work, intensified the scientific debate but have not yet led to a reclassification.
But were the results reproducible?
The World Health Organization and other bodies called for independent verification. The Korea–Japan collaboration answered that call.
Starting in 2019, teams from the Electronics and Telecommunications Research Institute, Ajou University School of Medicine, the Korea Institute of Toxicology, and partner institutions in Japan launched parallel experiments. They used the same strain of rats, the same food, the same exposure chambers, and the same protocols—closely modeled on the U.S. study but focused on exposure levels that underpin human safety standards.
Each group of 70 male rats lived inside reverberation chambers for 104 weeks, roughly their entire lifespan. One group received RF exposure from 900-megahertz CDMA signals at 4 watts per kilogram. Another experienced sham exposure—identical conditions, no radiation. A third lived as standard controls.
When the animals died or reached the end of the study, pathologists examined their organs in detail, with reviews conducted independently in both countries and verified by outside experts.
The results were very consistent. Tumor rates in exposed rats closely matched those in control groups. Where tumors did appear, they fell within normal background ranges for the species. Professor Young-Hwan Ahn of Ajou University, the study’s lead investigator, summed up the finding plainly:
“The tumor increase reported by the NTP was not replicated at exposure levels that form the basis of human protection standards.”
Reading the Results Carefully
The new study doesn’t erase the earlier U.S. results, but it does narrow their interpretation.
The National Toxicology Program exposed rats to RF levels as high as 6 watts per kilogram—higher than typical human exposure from phones. The Korea–Japan project focused on 4 watts per kilogram, a benchmark considered to be safe.
At that level, the researchers found no statistically significant increase in tumors or measurable genotoxic effects, including in sensitive tissues such as the brain and heart. This suggests that the existing limits are healthy and really do work.
Yong-Beom Kim, who oversaw pathological analysis at the Korea Institute of Toxicology, emphasized the safeguards built into the work. “The objectivity of the pathological evaluation was secured through mutual verification by experts from both countries and an international third-party peer review,” he said.
At exposure levels aligned with existing safety standards, this large, carefully controlled experiment found no sign that mobile phone RF signals trigger cancer in rats.
The research effort continues. New technologies, including 5G, create more complex exposure environments. The Korean team has already signaled plans for follow-up studies.
After years of uncertainty, scientists put one long-standing fear to an unusually exacting test—and this time, the evidence did not support it.
