Nothing seems to unite our common hysteria more than news that cellphones just might, in rare circumstances, in just a few people, have something to do with cancer. This week, the International Agency for Research on Cancer, a panel of the World Health Organization, listed the electromagnetic fields emitted by cellphones as being "possibly carcinogenic." Those cooler minds who took the time to read IARC's report by the light of their cellphone bonfires realized that there wasn't much to be afraid of.
When you dig into this issue, the IARC's decision seems to be an over-cautious interpretation of the current understanding of cellphones and our brains. That's OK—the panel is known for its extreme caution, and it listed cellphones in its lowest-risk category of potentially carcinogenic agents, a classification that requires only "limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals." So far, there's very little in the research about cellphones and cancer to suggest we should consider them to be among the more deadly products we come into contact with every day.
Yet the reaction to the WHO study—and, more generally, the decades-long panic over the possibility of cellphones causing cancer—suggests we're irrationally scared about this possibility. Lawmakers in California, Maine, New Mexico, Oregon, and Pennsylvania are pushing bills to add warning labels to cellphone packages. Last year, the city of San Francisco passed a measure requiring retailers to post the radiation levels of every cellphone model they sold, and several other cities across the country are considering similar policies. These laws are bizarre—we don't go around requiring warning labels on the many more deadly products we use all the time. You'd be surprised how much radiation you absorb on a five-hour flight, for example. Our worries about cellphones and cancer clearly aren't based on a rational analysis of their relative risk compared with other products we use.
Why do we reserve special fear for our phones? I suspect it's because they're new, and they're everywhere. In a very short time, cellphones have infiltrated every inch of our lives, totally upending how we conduct our closest social relationships. As they become more omnipresent, they become more indispensible every day. We can't live without them, but we all occasionally yearn for the days before these blasted things were invented. The paranoia over cancer reflects this sudden, uneasy intimacy: What if these alien devices are silently killing us?
As best as we can tell, they're not. Let's look at the science. When people worry about the dangers of cellphones, they're mainly referring to three kinds of tumors—acoustic neuroma, meningioma, and the most common and the most deadly form of brain cancer, glioma. * Over the last decade, there have been several extensive studies of the effects of cellphones on all three of these forms of tumors. (The IARC's classification deals only with gliomas.) In a press conference [MP3], Jonathan Samet, an epidemiologist at the University of Southern California and the chairman of the panel that made the classification, said that the group was heavily influenced by a study conducted by a group called Interphone. The research, which focused on gliomas and meningiomas, was the largest and most recent study on how cellphones affect the brain. It was conducted by researchers across Europe and funded by European governments and cell phone industry groups; researchers were given scientific independence over their findings. The trouble is, Interphone's results were wildly inconclusive—and, according to its own authors, the study was most probably flawed.
In one sense, the results of the Interphone study [PDF] are very comforting: The researchers found that people who called themselves "regular users" of cellphones (meaning they conducted at least one call a week for a period of more than six months) were less likely than people who didn't use cellphones to develop gliomas and meningiomas. That's right—the study, which compared 2,708 glioma patients and 2,409 mengioma patients with a matched group of people who didn't have cancer, found that, in many ways, using a cellphone seemed to reduce your risk of cancer. This finding held true for almost every way that researchers sliced the data. People who used cell phones for more than 10 years had almost 20 percent lower odds of developing a meningioma, and a 2 percent lower chance of developing a glioma, than people who didn't use cellphones. People who reported having made more than 27,000 cellphone calls in their lives also had lower odds of developing both cancers than non-cellphone users. (See Page 6 in the report.)
There was only one category of users in the Interphone study for whom cellphones seemed to pose an increased risk: People who reported having spent more than 1,640 hours of talk time without using a hands-free headset. (They were probably on your train car.) Compared with nonusers of cellphones, these extremely heavy users saw a 15 percent increase in the odds of developing a meningioma and a 40 percent increase in the odds of developing a glioma.
Taken together, these findings look suspicious. The story they tell about cellphones and cancer doesn't make any kind of medical sense—you'd have to believe that for most users, mobile phones seem to confer some kind of benefit against cancer, but that when you pass more than 1,640 hours of use, they suddenly turn deadly. In their paper reporting these findings, the researchers rained on their own parade, explaining that both conclusions about phones (that they somehow reduce the risk of cancer for most users, and increase the risk for heavy users) were probably the result of various research biases. Of the finding that cell phones cause cancer in heavy users, the researchers wrote that "biases and errors limit the strength of the conclusions we can draw from these analyses and prevent a causal interpretation."
Many other studies have offered similarly confounding results. See this list of the major investigations of cellphones and cancer conducted over the past decade—nearly every one shows that cellphone use has either no effect or reduces the odds of developing cancer. You may argue that these don't tell the whole story. As Siddhartha Mukherjee pointed out in the New York Times Magazine in April, finding the connection between a rare form of a cancer (like brain cancer) and a very common potential risk factor (like cell phones, of which there are now more than 5 billion in use worldwide) is an extremely difficult epidemiological task. Researchers looking into the links between cancer and phones face many ethical and logistical hurdles—among them, that mobile phones may be too new to have caused any effects yet, and that there's a smaller and smaller population of non-cellphone users to study as a control group. Over time, with deeper research, it's certainly possible that we might find some increased risk.
But it's wise to keep that possibility in perspective. The overall incidence of brain cancer is very low, so if it's proven, eventually, that mobile phones increase your risk, they may still be relatively safe. For instance, in Europe and North America, the incidence of glioblastoma multiforme, the most aggressive malignant brain tumor, is between two and three new cases per 100,000 people per year. If we assume that the most alarming findings from the Interphone study are true—that heavy users face a 40 percent increase in the chance of developing gliomas—this amounts to just one extra case of glioblastoma per 100,000 people per year.
To me, that sounds like a very small increase in risk. When it comes to cancer, you likely face more danger going out into the sun than you do on a cellphone. Indeed, risk of getting cancer from a phone seems, at most, to be on the order of other freak but otherwise minimal dangers of modernity—the risk of getting strangled on window-blind cords, of choking on a hot dog, or getting injured in a while playing in a bouncy house. When we hear about these things, we fret, but we don't freak out. That's how you should regard cellphones, too. Yes, they're new and scary. But there's no reason to panic—so long as you're not trying to drive at the same time as you talk.
Correction, June 3, 2011: This article misidentified acoustic neuromas as a cancer; they're brain tumors that can be dangerous but aren't malignant. (Return to the corrected sentence.)
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