A government study released today on cell-phone radiation and cancer has found a slight connection between the two: High exposure to such radiation caused malignant tumors to grow in the nerves and hearts of male rats, but not in female rats, and not in any of the mice tested.

The link between cell-phone radiation and malignant brain tumors called gliomas was weaker. Gliomas were detected in male rats exposed to radiation, but it was unclear whether or not those tumors were actually caused by the radiation.

The study, which cost $25 million and took more than a decade to complete, was conducted by the National Toxicology Program, a division of the National Institutes of Health. It is the largest study to date on the question of whether cell phones can cause cancer, and will undergo a final peer review by a group of outside experts at the end of March. But its conclusions are unlikely to resolve a long-standing and sharp debate over the relative safety of modern society’s most ubiquitous piece of technology.  

More On Radiation and Cancer

That debate has divided health agencies and organizations around the world, not to mention scientists, the cell-phone industry, and consumer-safety advocates.

The Food and Drug Administration says that the research to date (this most recent study included) indicates that cell phones are safe. “Based on this current information, we believe the existing safety limits for cell phones are acceptable for protecting the public health,” says Jeffrey Shuren, M.D., J.D., director of the FDA’s Center for Devices and Radiological Health. “Taking into account all available scientific evidence we have received, we have not found sufficient evidence that there are adverse health effects in humans caused by exposures at or under the current radiofrequency energy exposure limits.”

And Justin Cole, assistant vice president of public affairs for CTIA, a trade group for the wireless industry, pointed out that numerous organizations, including the FDA, the American Cancer Society, and the Federal Communications Commission, have long concluded that there is no proven health risk associated with radiation emitted by cell phones.

However, some experts do worry about the potential risks of cell-phone radiation. The International Agency for Research on Cancer classified cell-phone radiation as a possible human carcinogen in 2011, and in May of 2015, a group of 190 independent scientists from 39 countries called on the United Nations, World Health Organization, and others to subject cell phones to stricter safety controls.

Consumer Reports health and safety experts believe that while the evidence of a link between cell-phone use and cancer is still far from clear, the new findings highlight the need for continued research into the possible effects of cell phones on human health, and underscore our long-standing advice to follow some basic precautions when using the devices.

What the New Study Found

Rats and mice (roughly 3,000 total) were exposed to the same kind of radiofrequency waves emitted from cell phones, for 9 hours each day, spread over the course of the day. The exposure to that radiation began in utero and continued for about two years. Because rodents develop cancer much faster than humans, two years is enough time to reveal longer-term cancer risks (a 2-year-old rat is roughly equal to a 70-year-old human).

The study used specially designed chambers that allowed researchers to expose rodents to standardized doses of radiation. The radiation frequencies and signal modulation used were the same used by 2G (GSM or CDMA) phones, which were standard when the study began. Newer cell phones use 3G (such as UMTS or CDMA-2000) or 4G (LTE), which may have lower power outputs and different signal modulation, making the relevance of the findings to current phones uncertain.

The most alarming finding was this: Six percent of male rats exposed to radiation (but zero percent of those not exposed) developed malignant heart tumors called schwannomas. The incidence of those tumors increased as the rats were exposed to higher doses of radiation, suggesting that the radiation was responsible.

But neither female rats nor mice of either gender developed such tumors, even when they were exposed to radiation. What’s more, the rats that developed tumors lived longer on average than those that did not. Scientists have been at pains to explain these caveats since 2016, when the preliminary report was published; today's final report did not resolve them.

NTP senior scientist John Bucher, Ph.D., says that while the heart tumors found in the current study are similar to certain brain tumors found in some human epidemiological studies of frequent cell-phone users, the rodent findings should be interpreted with caution. “The levels and duration of exposure to RFR were much greater than what people experience with even the highest level of cell-phone use, and exposed the rodents’ whole bodies,” he says. “So, these findings should not be directly extrapolated to human cell-phone usage.” 

How to Play It Safe

Consumer Reports health and safety experts say that while it is far from clear whether or how much cell-phone radiation impacts human health, it’s worth taking some simple steps to limit your exposure and reduce the potential risk.

Specifically, Consumer Reports recommends that you:

  • Try to keep the cell phone away from your head and body. Keeping it an arm’s distance away significantly reduces exposure to the low-level radiation it emits. This is particularly important when the cellular signal is weak—when your phone has only one bar, for example—because phones may increase their power to compensate.
  • Text or video call when possible, because that allows you to hold the phone farther from your body.
  • When speaking, use the speakerphone on your device or a hands-free headset.
  • Don’t stow your phone in your pants or shirt pocket. Instead, carry it in a bag or use a belt clip.

What Government and Industry Should Do

The ongoing questions raised by this and previous research regarding cell phones and cancer requires decisive action by the government and industry. Specifically, Consumer Reports believes that:

  • The National Institutes of Health should commission another animal study using current cell-phone technology to determine whether it poses the same risks as found in this new study. Such follow-up studies will be especially important now that 5G technology is poised to dramatically increase the number of transmitters sending signals to cell phones.
  • The Federal Communications Commission should update its requirements for testing the effect of cell-phone radiation on human heads. The agency's current test is based on the devices’ possible effect on large adults, though research suggests that children’s thinner skulls mean they may absorb more radiation. The FCC should develop new tests that take into account the potential increased vulnerability of children.
  • The FDA and the FCC should determine whether the maximum specific absorption rate of 1.6 W/kg over a gram of tissue, the current standard, is an adequate maximum limit of radiation from cell phones.
  • The Centers for Disease Control and Prevention should repost advice on the potential hazard of cell-phone radiation and cautionary advice, which was taken down in August 2014.
  • Cell-phone manufacturers should prominently display advice on steps that cell-phone users can take to reduce exposure to cell-phone radiation.