Using a mobile phone may increase your risk for certain kinds of brain cancers. That was the scientific conclusion relayed today by a working group of 31 scientists from 14 countries meeting at the World Health Organization’s International Agency for Research on Cancer (WHO/IARC) who completed a review of the available scientific evidence on cell-phone radiation and brain tumors.
The group, which is working on a research monograph that will soon be available, classified cellphones in the carcinogenic category 2B, similar to chemicals like the pesticide DDT and gasoline engine exhaust. In slightly clearer terms, that means cell-phone radiation is “possibly carcinogenic” to human beings. “A review of the human evidence of epidemiological studies shows an increased risk of glioma and malignant types of brain cancer in association with wireless-phone use,” Dr. Jonathan Samet, the chairperson of the IARC working group, told reporters today.
(More on TIME.com: 5 Easy Ways to Reduce Your Cell Phone Exposure)
It’s not clear exactly how much of an elevated cancer risk cell-phone users might face, or even the biological methods by which cell-phone radiation could cause brain tumors. (The radiation emitted by cell phones is non-ionizing, meaning that it shouldn’t have enough energy to damage body tissue the way that ionizing — and carcinogenic — X-ray radiation can.) But IARC says that the results of epidemiological studies of cell-phone users, including the data from last year’s rather problematic Interphone study, indicate an association between handset use and tumors.
That’s notable because until now, the WHO had reported that “no adverse health effects have been established for mobile-phone use.” (In fact, that website is still up.) While medical muckrakers like Dr. Devra Davis, who wrote a 2010 book on cell phones and cancer called Disconnect, and academics like Dr. Henry Lai have questioned the possible role that cell-phone radiation could play in brain tumors, the mainstream medical establishment has all but dismissed any risk, along with most governments including the U.S.
(More on TIME.com: Study: Cell Phones Cause Changes in Brain Activity)
The IARC statement (download a PDF of the group’s statement here) could change that. “This is the first real review of the evidence on data of cancer,” said Dr. Kurt Straif, head of the IARC monographs program. “That WHO position was before the outcome of this meeting was ready. Therefore, the WHO will probably look into this and see what it should do.”
For those who’ve warned of the potential dangers of cell-phone radiation, like Davis, the IARC conclusions look like validation. As Davis wrote to me in an email today:
We should follow the positions taken by the tech-savvy Israelis and Finns, and urge simple precautions to keep cell phones from the brain and body, adopting the ALARA principle (from radiation biology) — As Low as Reasonably Achievable — of technology…
Cell phones have revolutionized our lives and we need to be sure that they are used as safely as possible and that people are advised on simple ways to protect themselves and their families.
For his part, Straif noted that while the IARC wasn’t making any judgment about the actual risk level of using cell phones, those who wished to minimize exposure to radiation could simply text instead of calling, or use wired hands-free headsets for any calls. (See 5 easy ways to reduce your exposure here.) “At the moment it is not clearly established that the use of mobile phones does cause cancer in humans,” said Straif. “But there are clearly some ways about how to reduce exposure.”
(More on TIME.com: 6 Common Sources of Radiation In Your Life)
Still, the IARC’s conclusions came as a surprise to many researchers — especially after last year’s multi-country Interphone studies (which cost $24 million and included more than 12,000 participants) seemed to indicate that there wasn’t an increased risk of brain cancer from cell-phone use, outside the heaviest users. In 30 studies done in Europe, New Zealand and the U.S., patients with brain tumors did not report using their cell phones more often than unaffected subjects.
Dr. David Savitz, an epidemiologist at Brown University who has studied cell phones and cancer, notes that there has been no obvious uptick in brain cancer rates in the two decades since cell phones went from zero to some 5 billion subscriptions around the world. “It’s possible that in 10 or 20 years things could unfold differently,” Savitz told me. “Nonetheless everything I have seen so far points in the opposite directions [of IARC’s conclusions].”
Even the IARC researchers noted that they were drawing on epidemiological studies from about the mid-1990s to 2003-04 — and that both cell-phone technology and cell-phone use had changed immensely in the years since. Studies have shown that teenagers, for instance, now text and use their phones for apps more often than they call.
A study earlier this year from the National Institutes of Health found that cell-phone use can change brain activity, but it’s still far from clear what that actually means, which just adds to the mystery. “We don’t know what may happen as people use their mobile phones longer and longer,” said Samet. “We need to track as best as possible the kind of phones people actually use.”
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Indeed, the lasting conclusion from the IARC monograph is that we need more research — and more research we will get. “This review represents an important first look by IARC at an exposure that is transforming the world,” said Samet. “I’m sure there will be another monograph [on the subject] in the future.” Of that, there can be no doubt.