Cell-Phone Radiation Can Cause Cancer in Rats. The Next Question: What Does it Mean For Humans?

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The studies were nearly two decades in the making.

The U.S. government released the final conclusions Thursday, Nov. 1 of a pair of federal studies that show “clear evidence” that cell-phone radiation is linked to heart cancer in male rats.

The studies, conducted by the U.S. National Toxicology Program, also found “some evidence” that the radiation is linked to brain cancer and adrenal gland cancer in male rats. (The NTP uses the labels “clear evidence,” “some evidence,” “equivocal evidence” and “no evidence” when making conclusions.)

The studies, nearly two decades in the making, went through a rigorous peer-review process in March.

It is important to note that animal studies can’t perfectly replicate human cell-phone use, which includes holding a phone to your ear or carrying one in a pocket. And the levels of radiation the rodents were exposed to for these studies were higher than a human normally would be exposed to by using cell phones—the lowest exposure level used in the studies was equal to the maximum exposure allowed by U.S. regulators for cell phone users, which is a power level that “rarely occurs” with typical cell phone use, according to the NTP. The highest level of radiation the rats were exposed to was four times higher than the maximum level permitted.

“We believe that the link between radio frequency radiation and tumors in male rats is real,” John Bucher, a senior scientist at the NTP, said in a statement.

Tumors were also found in the hearts of female rats, but the researchers said they couldn’t be sure the radiation is what caused the tumors.

A new turn in the debate

As we’ve noted before, these results substantially change the debate on whether cell-phone use is a cancer risk at all. Up until this point, the federal government and phone manufacturers operated on the assumption that cell phones cannot by their very nature cause cancer, because they emit non-ionizing radiation. Ionizing radiation—the kind associated with Xrays, CT scans, and nuclear-power plants, among others—definitely causes cancer at high enough doses. Non-ionizing radiation was believed to not emit enough energy to break chemical bonds. That meant it couldn’t damage DNA, and therefore couldn’t lead to mutations that cause cancer. But these conclusions upend that assumption.

The rats were exposed 2G radiation, the globally prevalent cell-phone technology when the studies were designed in the 1990s, which operates on the radio frequency of 900 megahertz. In the U.S., several service providers have turned their 2G service off. Others, like Verizon, plan to soon. Even as its use wanes in Europe and North America, 2G is still widely present in Africa and South America.

Cell phones in the U.S., Europe, and Asia operate mostly on 3G and 4G technology, with 5G likely to penetrate the market soon. Each generation employs a different frequency, many of which are higher frequencies than 2G’s 900 megahertz. Higher frequencies penetrate the bodies of humans and rats less successfully, according to research highlighted by the New York Times.

What comes next

The next scientific step will be to determine what the studies’ results mean for humans. The peer-reviewed papers will be passed onto the U.S. Food and Drug Administration, which is responsible for determining human risk and issuing guidelines to the public, and the Federal Communications Commission, which develops safety standards for phones. The FDA was among the federal agencies that commissioned the studies in the early 2000s.

Ronald Melnick, the NTP senior toxicologist who designed the studies (and who retired from the agency in 2009), told Quartz following the March peer-review process that it’s unlikely any future study could conclude with certainty that there is no risk to humans from cell phone use. “I can’t see proof of a negative ever arising from future studies,” Melnick said.

He believes the FDA should put out guidance based on the results of the rat studies. “I would think it would be irresponsible to not put out indications to the public,” Melnick said. “Maintain a distance from this device from your children. Don’t sleep with your phone near your head. Use wired headsets,” he said, which emit less radiation. “This would be something that the agencies could do right now.”