Radiation Risk: Are Some Cellphones More Dangerous Than Others?

Phones that use GSM networks emit more radiation than phones on CDMA networks. Credit: sxc.hu | apatterson — Phones that use GSM networks emit more radiation than phones on CDMA networks.

(Image credit: sxc.hu | apatterson)

Last month, the International Agency for Research on Cancer, a branch of the World Health Organization, declared cellphone radiation "possibly carcinogenic to humans." The scientific evidence linking cellphone use to brain cancer isn't conclusive, the agency said, but there is some evidence that brain cancer rates are higher among people with the highest levels of cellphone exposure, and cellphone users should take precautions until more is known.

Now, some scientists are claiming that certain types of cellphones could be more "possibly carcinogenic" than others.

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There is accumulating evidence that cellphones that operate on GSM networks emit significantly more radiation than do cellphones operating on CDMA networks. This is not apparent when you look at a phone's specs, Moskowitz said, because phone companies are required to list only the "specific absorption rate" (SAR) — the measure of the rate at which energy from a radio frequency electromagnetic field is absorbed by the body — of a phone at its maximum radiation output. "The SAR can be misleading as it measures the maximum radiation a cellphone emits and does not reflect the average amount of radiation it emits," Moskowitz told Life's Little Mysteries.

"When a GSM phone transmits, it immediately goes to the peak power, and then the power control circuitry ratchets down the power to an acceptable level," explained Mark McNeely, an electrical engineer at Exponent Engineering and Scientific Consulting services and co-author of a recent study comparing GSM and CDMA networks. "CDMA networks share the same frequency among many different phone calls, so all phones transmit at the lowest possible power level necessary to maintain the fidelity of the call." It's like people talking quietly at a party, he said.

There are exceptions. If you have a CDMA phone in a rural area and the nearest CDMA cellphone tower is far away, then you have to broadcast at a radiation level that is equal to or greater than GSM to reach the tower, McNeely said. If there is a GSM tower much nearer to you, you might be better off going with a GSM network, he said; but in most parts of the country, where both CDMA and GSM towers are ubiquitous, CDMA phones will emit less radiation than GSM phones.

Although it's still unclear what that extra brain activity is, how it's caused or whether it's bad, other studies have also shown varying health consequences of using GSM versus CDMA phones. Of 37 studies that have examined GSM phones, 43 percent have found harmful biological effects from the phones — such as a decrease in the expression of genes that help suppress tumors — Moskowitz said, while only 15 percent of the 33 studies that looked at CDMA phones have identified harmful effects.

When reached for comment on the possible hazards of GSM phones, AT&T referred to previous statements by the Federal Communications Commission and the Food and Drug Administration that said the available scientific evidence shows no proven health risk of radiofrequency (RF) energy. The FDA states: "Although evidence shows little or no risk of brain tumors for most long-term users of cellphones ... people who want to reduce their RF exposure can: reduce the amount of time spent on the cellphone, and use speaker mode or a headset to place more distance between the head and the cellphone." T-Mobile did not return telephone calls or emails.

It is difficult to say whether higher radiation output is bad, simply because the jury is still out on whether cellphone radiation is bad in the first place, says Ken Foster, a professor of bioengineering at the University of Pennsylvania who has been studying the effects of radiofrequencies for 40 years. The radiation level of cellphones — all cellphones — is so low it is considered "non-ionizing." It isn't powerful enough to knock electrons off atoms in cells and potentially change the structure of DNA molecules, which is the way that ionizing radiation (like gamma-rays and X-rays) causes harmful mutations. No one knows by what mechanism non-ionizing radiation, such as RF from cellphones, could possibly damage DNA, Foster says.

If cellphones are a biohazard, Foster said, that can't be related to the amount of the radiation they emit. "Presumably, some parameter other than [radiation output] would be involved." No one has identified what aspect of cellphone radiation is dangerous, Foster said, so there is no way of knowing whether GSM phones are worse for you than CDMA phones, or vice versa. [Read: What Everyday Things Around Us Are Radioactive?]

However, according to other scientists, there is some evidence that the potentially hazardous aspect of cellphone radiation may be the way in which transmissions are modulated — the way individual pulses of radiation are constructed out of a range of frequencies. The modulation pattern is different for CDMA and GSM phones, and some scientists think GSM pulse modulations may have adverse biological effects.

Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.