According to a 10-year study by the National Institutes of Health (NIH), it causes various types of cancers from the heart to the brain. The participants of the collaboration plans to conduct another series of experiments, in which they will keep track of the changes in the rate of accumulation of DNA mutations rodents and how often they appear in other traces of cancer.
"The exposures used in the studies can not be compared directly to the exposure that humans experience when using a cellphone", John Bucher, a senior scientist with the U.S. National Toxicology Program (NTP) and co-author of the study, said in a statement.
Still, the researchers said their findings question the long-held assumption that the radio-frequency radiation used by cellphones poses no health concern.
"The incidence of brain tumors in human beings has been flat for the last 40 years", Brawley said.
However, those tempted to toss away today's most important tool of communications may want to consider that the study's researchers did specify the levels of radiation the rats were subjected to were not comparable to those humans are exposed to. But he cautioned that the exposure levels and durations were far more significant than what people typically encounter, and thus can not "be compared directly to the exposure that humans experience".
According to the US Food and Drug Administration (FDA), while animal studies contribute to discussions on the topic, "this study was not created to test the safety of cell phone use in humans, so we can not draw conclusions about the risks of cell phone use from it". Additionally, cardiac Schwann cell hyperplasia occurred in groups of male rats exposed to both GSM- and CDMA-modulated cell phone RFR.
Currently, 95 percent of American adults use cellphones.
Some 2- 3 per cent of the male rats exposed to the radiation developed malignant gliomas, a deadly brain cancer, compared to none in a control group that received no radiation.
On Nov. 1, a federal health panel found that male rats can get cancer from high doses of cell phone radio waves, but those doses of radio waves were four times higher than what a 2G or 3G cellphone emits when you're using it, BuzzFeed News reports.
Some scientists have warned that 5G - which uses milimeter waves, rather than the microwaves that were the basis of previous generations - may in fact be more risky, but its far too soon to tell for sure.
The rats were exposed to radiation at a frequency of 900 megahertz, typical of the second generation of cellphones that prevailed in the 1990s, when the study was first conceived.
The levels the rodents experienced were far higher than people are typically exposed to.
Current cellphones are considered a fourth generation, known as 4G.
The NTP researchers are planning future studies on the effects of newer technologies, and these studies will use different methods so that they will be completed in weeks to months, rather than years.
"As scientists, we welcome new studies", Shuren said.
In June, at a meeting of scientific counselors to the toxicology agency, Donald Stump, one of the members, anxious that the study "will be vulnerable to criticism that it was conducted using outdated technology". The lowest level of radiation used was the maximum exposure allowed for cellphone users by federal regulations.
Those who study risk aren't hanging up.