Ever since mobile phones first appeared, well before they evolved into “smartphones,” public apprehension has existed regarding their signals potentially causing health issues. While numerous studies have generally indicated they are entirely safe, a high-profile report released in 2018 by the US National Toxicology Program reignited these concerns.
So, do phones actually pose a danger? A fresh, extensive international study, with its findings published by Oxford Academic, suggests the answer is definitively no.
In a coordinated experiment spanning multiple nations and covering various stages of the rats’ lives, researchers from South Korea and Japan found no significant correlation between prolonged exposure to mobile phone radiofrequency signals and the development of tumors in the brain, heart, or adrenal glands.
The results of the 2018 report caused a stir, and it wasn’t the sole study raising red flags. Radiofrequency radiation has been classified as “possibly carcinogenic” since 2011, the year the International Agency for Research on Cancer reviewed the field. Subsequent research, including work by the National Toxicology Program (NTP), intensified the scientific debate but has not yet resulted in reclassification.
But were those earlier findings reproducible?
The World Health Organization and other bodies called for independent verification. The Korean-Japanese collaboration answered this call.
Beginning in 2019, teams from the Electronics and Telecommunications Research Institute, Ajou University School of Medicine, the Korean Institute of Toxicology, and affiliated institutions in Japan initiated parallel experiments. They utilized the same rat strain, identical feed, shared exposure chambers, and the same protocols—largely modeled after the US study but concentrating on exposure levels that underpin human safety standards.
Each cohort, consisting of 70 male rats, was housed in reverberation chambers for 104 weeks, which approximates their entire lifespan. One group was subjected to radiofrequency radiation from 900 MHz CDMA signals at a power level of 4 watts per kilogram. A second group received sham exposure—under identical conditions, but without radiation. A third group was kept under standard control conditions.
Upon the animals’ demise or the study’s conclusion, pathologists meticulously examined their organs, with independent evaluation conducted in both countries and confirmed by external experts.
The outcomes proved highly consistent. The incidence of tumors in the exposed rats was nearly identical to the rates observed in the control groups. Where tumors did appear, their frequency remained within normal background levels for that species. Professor Young-Hwan Ahn of Ajou University, the lead investigator of this research, succinctly summarized the findings: “The increase in tumors reported by the NTP was not observed at exposure levels underpinning human protection standards.”
The new research does not negate earlier US findings, but it refines the scope of their implication.
As part of the National Toxicology Program, rats were exposed to radiofrequency radiation up to 6 watts per kilogram—exceeding typical human exposure from phones. The Korean-Japanese project focused on 4 watts per kilogram, which is deemed safe.
At this level, researchers identified no statistically significant rise in tumor counts or any measurable genotoxic effects, including within sensitive tissues like the brain and heart. This implies that current safety limits are sensible and effectively protective.
Young-Bum Kim, who oversaw the pathological analysis at the Korean Institute of Toxicology, emphasized the precautions embedded in the work. “Objectivity in the pathological assessment was ensured through mutual verification by experts from both nations and international independent expert review,” he stated.
In this large-scale, strictly controlled experiment, using exposure levels consistent with existing safety benchmarks, no evidence emerged suggesting that mobile phone radiofrequency signals cause cancer in rats.
Research efforts are ongoing. Emerging technologies, including 5G, present more complex exposure scenarios. The Korean team has already announced plans for follow-up investigations.
After many years of uncertainty, scientists subjected one of the most persistent public fears to an exceptionally rigorous test—and this time, the evidence did not support it.
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