It’s been one of the most visible technological revolutions since the coming of the automobile: the liberation of telephones from stationary land lines to mobile models; the proliferation of hand-held phones in workplaces, in homes and on the street; the explosion of enhanced versions to send texts, take pictures, play music, guide people through their day. By now an estimated four billion people around the world use cell phones.

Undergirding the wild success of these products has been something less explicit than a guarantee, just a trust—for would enlightened governments allow corporations to put something dangerous on the mass market?—that the devices were safe to use. Study after study, usually industry-funded, said there was only minimal risk. So the image of the millennial city is an image of people walking along streets and in and out of buildings with miniaturized phones to their ears, and laws are in the making to keep us from crashing our cars while we’re talking or texting.

Now that cell phones are a fixture in our lives, new information—and old information breaking out after years of enforced silence—suggests that we need to rethink the matter of their safety. Consider this:

*Findings of Swedish researchers published in 2007 in the journal Occupational and Environmental Medicine showed “a consistent pattern of increased risk for acoustic neuroma [a benign tumor of the nerve connecting the brain and the ear] and glioma [a tumor originating in the brain’s glial cells].”

*In Israel, a study published in 2008 found that cell phone users had a 50 percent greater chance of developing benign or malignant tumors of the salivary gland than non-users.

*Also in 2008, the Royal Society of London published findings that people who begin using cell phones before age 20 were five times more likely as non-cell phone users to have brain cancer by age 29.

But it’s not only information that’s surfaced within the last few years that’s given impetus to new cautions about cell phone use. Investigation of the health effects of electromagnetic radiation goes back decades—and for decades there have been moves to downplay if not suppress it.

In 1975, neuroscientist Allan Frey went public with research showing that microwaves could cause breaching of the blood-brain barrier. That’s dangerous because the barrier protects the brain from many toxins and bacterial infections. Eventually Frey, who had received research funding from the Navy since he had begun experimenting with radar waves in the 1960s, was told he would lose his funding if he continued to publish his findings on the blood-brain barrier. (In those days, the military thinking on electromagnetics was based on the idea that only the thermal effects of the radiation were potentially harmful.)

In 1986, Carl Blackman, a highly credentialed physicist working for the federal Environmental Protection Agency, was ordered to stop his research on the health effects of electromagnetic radiation, which built, in part, on Frey’s findings. Blackman told GQ reporter Christopher Ketcham he suspects that “a decision was made to stop the civilian agencies from looking too deeply into the nonthermal health effects from exposure to EM fields.” Ketcham also quotes an unnamed EPA physicist as saying, “The Department of Defense didn’t like our research because the exposure limits that we might recommend would curtail their activities.” (Ketcham’s article, “Warning: Your Cell Phone May Be Hazardous to Your Health,” in the February, 2010 issue of GQ and available on the Web, should be required reading for all cell phone users.)

In the 1990s, Henry Lai, a bioengineering professor at the University of Washington, found that electromagnetic radiation damaged DNA in the brains of lab rats. His findings stopped short of proving conclusively that the DNA damage would produce cancer, but cancer was seen as a possible result of it. Motorola and other mobile phone companies mounted such a campaign to discredit findings of this nature that research efforts were muted for years to come.

Meanwhile, the industry funded a multimillion-dollar, six-year study that brought some unwelcome surprises. It confirmed that cell phone radiation caused breaching of the blood-brain barrier, interfered with normal DNA repair, and increased the risk of tumors in the tissues covering the brain and spinal cord.

Now studies by Dariusz Leszczynski at Finland’s Radiation and Nuclear Safety Authority also add to the body of information indicating that mobile phone radiation can damage the blood-brain barrier.

And experts are waiting for the result of a 13-country investigation of the health effects of cell phone use called the Interphone study (the 13 countries are Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden, and the U.K.; the U.S. did not participate). Some preliminary results of that study have been released; one finding incorporating information from Denmark, Norway, Sweden, Finland and the U.K showed a 40 percent increase in tumor incidence in adults who use cell phones for more than 10 years, though fewer than 10 years’ use was not found to cause significant risk.

But the results of the ambitious study, though they are nearly four years overdue, have not been released. In the U.S., the National Toxicology Program ( a program of the National Institutes of Health) is investigating the health effects of mobile phones, but results are not expected until 2014 at the earliest.

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The fragmentary nature of the available information about cell phones (which also applies to land-based cordless phones) and human health presents a daunting conundrum. What should users do until more definitive information is available? Experts aren’t suggesting that people throw away their cell phones, but that they use them in more safety-conscious ways.

Think twice before getting rid of your land line and its phones with cords; use those for your longer, leisurely conversations at home. When you buy a cell phone, read the manual that comes with it; some manuals warn users to keep the phones at least an inch away from their heads. The Federal Communications Commission limits the so-called specific absorption rate (SAR)—the amount of radiation the phone feeds into your body—at 1.6 watts per kilogram, but there’s debate about how much that really protects you. Nonetheless, the SARs of different models vary, and you might as well choose one with a lower rather than a higher SAR (to get the SAR of the phone you’re considering, check the packaging, ask the seller, or visit the FCC’s website, www.fcc.gov/cgb/sar/).

Don’t carry your cell phone near your body (in your pocket, for instance). A study from Hong Kong last year showed that even very low-level EMR fields affect sperm, and cell phones worn around the neck are suspected of causing heart attacks. Women, who usually stow the phones in their pocketbooks, probably incur lower risk. National Institutes of Health associate director Jon Bucher recommends using earpieces instead of holding the phones close to the head. Encourage children not to use cell phones except for emergencies, to major on texting rather than talking, and not to keep the phones under their pillows.