Feb 27 2014

Warning Labels on Cell Phones

Hawaii Senate Bill 2571, which is making its way through the legislature, would require that a large non-removable warning label be attached to the back of every cell phone. Originally the warning label was to read, “This device emits electromagnetic radiation, exposure to which may cause brain cancer. Users, especially children and pregnant women, should keep this device away from the head and body.” A revised version of the bill, however, changed the warning to, “To reduce exposure to radiation that may be hazardous to your health, please follow the enclosed product safety guidelines.”

This seems like an example of clear nanny-state overreach, but worse it is not based on science. According to reports every expert consulted by the relevant committees argued against the measure, but the legislators passed it anyway. The measure has one more committee to get through, and then it would go to the House for a vote.

As I have written before (see also here and here) there is no clear link between cell phone use and brain cancer. The plausibility of a link is low but not zero. Non-ionizing radiation is not energetic enough to break chemical bonds, and therefore should not cause DNA damage that could lead to cancer. However, an alternate physical mechanism cannot be ruled out, and biology is complicated, so I don’t think we can rule out a possible connection on theoretical grounds alone. We can just say it’s unlikely.

The National Cancer Institute summarizes the situation thusly:

It is generally accepted that damage to DNA is necessary for cancer to develop. However, radiofrequency energy, unlike ionizing radiation, does not cause DNA damage in cells, and it has not been found to cause cancer in animals or to enhance the cancer-causing effects of known chemical carcinogens in animals.

Epidemiological studies have been a little mixed, as is generally the case with this kind of evidence, but at this point the evidence is fairly solid that there is no link between cell phone use and brain cancer for exposure less than 10 years. The data for >10 years is less certain, but this is mostly because it takes more time to gather this data and we are just getting to the point that there is epidemiological evidence available for long exposures.

The NCI fact sheet also contains an excellent summary of all the relevant studies and the official opinions of various regulatory and health organizations. The bottom line is that there is no clear link. Epidemiological data cannot rule out a small connection, but it is reassuring when no clear signal is evident. This means, at worst, there is a small effect.

As is also often the case there are outliers. In this research I find one research group, Hardell and Carlberg, consistently find an association, at apparent odds with the rest of the scientific community. Some of their studies are also a little odd, like this one looking at brain cancer survival and cell phone use.  The results are all over the place, and their choice of statistical analysis seems a bit arbitrary. In other words, the data gives off a whiff a p-hacking. Without consistent independent replication, I usually do not put much weight on such outliers.

One other type of evidence that is relevant is the incidence of new cases of brain cancer. If cell phone use is a significant cause of brain cancer, then we would expect the incidence to be going up over the last 20 years as cell phone use has skyrocketed. However, the incidence has been stable to slightly decreasing. In the last 10 years the incidence of brain and other nervous system cancers has decreased on average by 0.2% per year. This is pretty strong evidence against any significant cell phone effect.

Other types of cancers have also been investigated. A recent study from Denmark showed no association between cell phone use and skin cancer. A possible association between carrying cell phone in one’s bra and breast cancer made the rounds in the media, but this is based on a case series of four patients. This is the most preliminary type of evidence, and should only be used as an indication for further research.


The scientific evidence does not point to any cancer or other health risk from cell phone use (unless you text while driving). The International Agency for Research on Cancer, American Cancer Society, National Institute for Environmental Health Sciences, the FDA, CDC, and FCC have all concluded that there is no clear evidence of any risk, although the IARC considers non-ionizing radiation a “possible” carcinogen.

Despite this Hawaiian politicians feel they know better and that they need to warn the public with a giant sticker on the back of every cell phone. If anything the sticker should warn about the risk of texting or using a cell phone while driving. That is a proven risk.

The evidence does not seem to rise to the level that an intrusive warning is indicated. The unintended negative consequence of such labels is warning fatigue. If the public is constantly bombarded with warnings of marginal or just possible risk, they will tend not to take such warnings seriously. They become part of the background noise. Then, when a warning would be actually beneficial, it is lost in this noise.

In this case, politicians should listen to scientists. If only.

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