The results of a new study by the National Toxicology Program—the largest and most expensive study of its kind—show a link between cell phone radiation and cancer in rats. 

For many people, these findings likely raise questions and concerns about the safety of devices that we now carry with us nearly all the time.

Consumer Reports health and safety experts, who have long been concerned about the potential risks of cell phones and urged precautions when using them, say the new study supports that caution.

"Consumers don’t need to stop using their phones," says Michael Hansen, Ph.D., a senior scientist with Consumer Reports who has studied this issue for years. "But there are some simple, common-sense steps you can and should take to reduce your exposure."

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 then to compensate.
  • Text or video call when possible, because this 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.

Below, answers to other basic questions about the study and what it means for you and your family.  

So What Did This New Study Find?

The study found that male rats had a higher incidence of two kinds of tumors when exposed to the same type of radiation emitted by cell phones.

The results are not conclusive, and the overall relevance to human cell phone use is something that’s “not currently completely worked out,” said John Bucher, Ph.D., associate director of the NTP, part of the National Institutes of Health.

But the new report adds weight to human epidemiological studies that have previously raised similar concerns, and when combined with those earlier studies, is poised to force a reconsidering among federal agencies of the potential risks posed by cell phones.  “In my experience,” Bucher said, “the people who have reviewed our findings agree with the findings.”

A spokesman for CTIA, a trade group for the wireless industry, says "Numerous international and U.S. organizations, including the U.S. Food and Drug Administration, World Health Organization, and American Cancer Society, have determined that the already existing body of peer-reviewed and published studies shows that there are no established health effects from radio frequency signals used in cellphones."

Why Should I Be Worried About a Study Using Rats?

Animal studies are actually the gold standard for determining cancer risk, for several reasons.

For one, it is unethical to expose humans to suspected carcinogens in a lab setting.

Second, studies in animals such as rats and mice can be completed much more quickly than they can be in humans, simply because their lifespans are so much shorter than ours. For example, the new NIH study involved exposing the rodents to cell phone radiation for just two years.

Finally, animal studies can validate results of previous observational studies in humans. Those studies, which track large groups of people over time, can look for associations between how many hours people said they used cell phones every day and the incidence of cancers in those people, but they can't prove a cause and effect relationship. Laboratory studies in rats, showing that exposure to cell phone radiation can cause cancers compared to a similar non-exposed group of rats, give credence to the results of observational human studies, and point strongly to cause and effect.

What Do Studies in Humans Show?

The current animal studies are worrisome precisely because they do line up with the results of some previous observational studies in humans.

Last year, Consumer Reports reviewed that research, focusing on five large population studies that investigated that question. Together the studies included more than a million people worldwide, comparing cell phone users with nonusers.

Three of the studies—one from Sweden, another from France, and a third that combined data from 13 countries—suggest a connection between heavy cell phone use and gliomas, the same kind of tumors detected in the new NIH study. Those tumors are usually cancerous and often deadly.

One of those studies also hinted at a link between cell phones and acoustic neuromas (noncancerous tumors); that kind of tumor is related to the second cancer detected in the current study, malignant schwannoma of the heart. 

An image of a brain cancer tumor.
This MRI shows a possible glioma in a human brain. The NIH study suggests cell phones radiation could cause that kind of cancer in rats.

How Might Cell Phone Radiation Cause Cancer?

Scientists previously thought that the radiation from cell phones might damage cells by heating human tissue. At high power levels radiofrequency waves—the kind emitted by cell phones—can heat up water molecules. Since human tissue is mostly water, scientists hypothesized that those waves might cause damage by heating.

The Federal Communications Commission’s cell phone emission test—which all cell phones must pass before being allowed on the market—is based on that principle.  

But in 2011, scientists at the NIH found that low level radiation, held close to the head, could alter brain cells without raising body temperatures. Likewise, in 2015, German researchers reported that the same type of radiation emitted by cell phones could promote the growth of brain tumors in mice without raising body temperatures.

The NTP study controlled for heating effects by making sure that the body temperatures of exposed rats did not increase by more than 1° C (1.9° F), suggesting that the cancers were triggered by some other mechanism.

Read our previous coverage about the potential dangers of radiation from cell phones and CT scans and X-rays.

How Well Does the NTP Study Mimic Current Cell Phone Usage?

The study used specially designed chambers that allowed researchers to expose rodents to standardized doses of radiation. The rodents were exposed for nine hours total each day, at intervals of 10 minutes on, 10 minutes off, for two years.

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.

“These changes may be a critical difference in whether there is a hazard today,” says Consumer Reports' Hansen. “But the study raises enough concern with the older technologies that we recommend an additional study be done with current technology.”

The rodents were exposed over their entire bodies. While that’s obviously different than the way humans use cell phones, the rodent results are still revealing, Hansen says.

“The reason we see schwannomas in the heart here, and not the auditory system, could be due to the fact that in rodents the heart is closer to the surface of the body,” he says. “What’s more important is that the cell type found in the heart in the NTP study is the same as in some brain tumors found in several human epidemiology studies.”

What Does Consumer Reports Think the Government and Industry Should Do Now?

The substantial questions and concerns raised by this and previous research regarding cell phones and cancer requires swift and 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 if it poses the same risks as found in this new study.
  • 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 Food and Drug Administration and the FCC should determine whether the maximum specific absorption rate of 1.6 W/kg over a gram of tissue is an adequate maximum limit of radiation from cell phones.
  • The Centers for Disease Control and Prevention should repost it’s advice on the potential hazard of cell phone radiation and cautionary advice that 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.