We Still Don’t Know If Cell Phones Cause Cancer or Not

American scientists released two new major studies investigating whether or not there’s connection between cancer risk and cell phone use and the much-awaited answer is…*drumroll, please*…we still don’t really know anything for certain.

The U.S.’s National Toxicology Program released the final results last week of two much-anticipated studies, one on mice and one on rats, which each exposed the animals to cell phone radiation at or above the U.S.’s legal limit for two years. The studies are part of a larger $25 million effort by U.S. federal agencies to assess the health risk of using cell phones.

Mobile phones emit non-ionizing radiation, measured in radio-frequency (RF) energy. While it is widely accepted in the scientific community that exposure to high doses of ionizing radiation—the kind associated with x-rays, CT scans, and nuclear power plants, among others—causes cancer, it is unknown whether long-term exposure to non-ionizing radiation is cancer-causing. Right now, most federal policies regulating cell phones assume it does not.

Both papers are scheduled for peer review in March—but the researchers have taken the unusual route of publishing drafts of their papers, due, they say, to the enormous public health implications. “Given the extremely large number of people who use wireless communication devices, even a very small increase in the incidence of disease resulting from exposure to the cell phone RFR [radio frequency radiation] generated by those devices would translate to a large number of affected individuals, which would have broad implications for public health,” they write.

For two years, researchers exposed mice and rats to radiation replicating 2G and 3G signal strength, which were the dominant and emerging technologies, respectfully, when the trials began several years ago. (In the papers, the researchers predict 2G will still be widely used globally for voice calling, even if it is on the decline in the U.S. Their next studies will look at 4G service, and they note even newer generations of cell phones—say, 5G—will operate at higher frequencies of radiation.)

What the studies actually found

The papers found that, in male rats, this exposure increased malignant tumors called schwannomas in the connective tissues that surround nerves in the heart, raised the risk of heart conditions, and led to evidence of DNA damage. Baby rats born to mothers during the trial had lower birth weights. The scientists also found a statistically significant increase in lymphoma (cancer of the lymph nodes) among female mice and heightened rates of liver cancer in the male mice.

Animal studies can’t perfectly replicate human cell phone use; you can’t make a rat hold a tiny mobile phone, and you certainly can’t recreate a lifetime of exposure like most people on Earth are experiencing now in a trial that’s just a few years long.

Meanwhile, it has been difficult to gather reliable human data on the relatively new phenomenon of cellphone use. The biggest cell phone-radiation study to date, the INTERPHONE study published in 2011, was a coordinated effort by researchers at 16 institutions across 13 countries. INTERPHONE found an increased risk for glioma, a malignant type of brain cancer, among the heaviest mobile phone users. But the study authors noted various problems with their data (it was based on interviews with people who already had brain cancer, so could be subject to recall bias) leaving plenty of uncertainty.

Plus, as researchers on the two new U.S. studies point out, the INTERPHONE scientists may have published their conclusions too soon to account for cancers that developed later; the lag time for the “development of slow-growing brain tumors” can take years to decades, the U.S. researchers note.

In response to the INTERPHONE report, the International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, classified radiation from cell phones as “possibly carcinogenic to humans” in 2011.

An earlier draft of the new U.S. study on rats, released in June 2017, agreed with that classification, noting that its findings “appear to support the [IARC] conclusions regarding the possible carcinogenic potential of RFR,” but that note does not appear in the newest draft.

Jonathan Samet, the dean of the University of Colorado-Denver School of Public Health who was lead investigator on the IARC working group that concluded that cellphone radiation was a “probable” carcinogen told Science the new U.S. studies won’t “nudge that classification in one direction or another.”

“I’m not saying there’s a public health crisis by any means,” Samet previously told the Verge, “but I’m saying here’s a very widespread exposure in our society and we should make sure we understand it.”

Some states aren’t waiting for conclusive results

In December, the California state health department released guidelines warning residents to avoid putting mobile phones up to their heads. The guidelines include a separate warning about childhood cell phone use, stating that “RF energy can reach a larger area of a child’s brain than an adult’s brain,” and the ills, if any, would “more harmful and longer lasting” in children than in adults.

Other states are proposing bills meant to address cell phone radiation, particularly in children; On February 3, Maryland introduced a bill in its state house to “develop health and safety guidelines” for “the use of digital devices in public school classrooms.” In Massachusetts, several bills have been introduced to deal with the potential dangers of radiation from wireless devices, including one to create a special commission to study exposure to electromagnetic fields; another to create best practices for managing wifi exposure wifi in schools (wifi relies on non-ionizing radiation, like cell phones); and a third, scheduled for a hearing in April, that would require prominent labels about radiation exposure on cell phone packaging.

Apple already tells you to keep your phone away from your body

As Quartz has explained before, in the manual that comes pre-installed on your iPhone, Apple explicitly tells you to use a hands-free option like speakerphone or headphones while talking in order to “reduce exposure to RF energy.” The manual also notes that cell phones are currently tested for radiation assuming the devices would be kept at least 5 mm (0.2 in) away from the body while being carried. That’s a lot more than the thickness of pocket fabric. (On an iPhone 6 and above, you can find this information by going to Settings > General > About > Legal > RF Exposure.)

Previous iPhone manuals were even more conservative: The manual for the iPhone 5 says users should carry their iPhones a full 10 millimeters (or 0.39 inches) away from their bodies at all times.

U.S. law demands that all cell phones function in such a way that they cause less than 1.6 watts of radiation to be absorbed by the human body, per gram of body tissue (known as specific absorption rate, or, in this case, SAR 1.6). The Federal Communications Commission (FCC) tests all mobile phones coming onto the market for compliance. But that rule is designed only to prevent harm from excess heat that can be generated by RF waves. It doesn’t consider (pdf) other potential biological effects, like DNA damage or altered protein expression—the FCC calls these all “ambiguous and unproven.”

Further, the FCC only tests cell phones against a simulated human head in the “talking” position, and not against the body (or in a pocket) in the “carrying” position. That’s because the tests assume the user is holding the phone away from the body whenever the phone is broadcasting at full power, like the manuals say they should. But it’s safe to say most people carry their phones in their hands or their pockets while they stream videos or music, or while they talk on the phone through a headset. Even the thickest pocket fabric isn’t thick enough to meaningfully reduce RF exposure. And since RF energy exposure increases sharply when your phone is in contact with or very close to your body, and falls off rapidly at a distance, some experts and organizations like the nonprofit Environmental Working Group worry that FCC testing is missing a lot of actual exposure.