|Fig. 1: A man holding a cell phone close to his head, which would be discouraged under new California Department of Public Health guidelines (Source: Wikimedia Commons)|
Over the last 10 years, cell phone use has become ubiquitous and essential to daily life, with over 6.9 billion subscriptions globally.  This dramatic societal transformation, however, has understandably brought up concerns about the radiation health risks of cell phones, especially since phones are kept on and near people for most of the day. Indeed, the California Department of Public Health released guidelines in December 2017 advising the public to reduce exposure to radio frequency energy from cell phones, citing studies that suggest the possibility that cell phone use may be linked to adverse health effects.  Guidelines included keeping phones away from the body when not in use and using speakerphones or headsets to make calls rather than holding phones to heads, as depicted in Fig. 1.  However, such conclusions have also been repeatedly contested and mostly rejected in the last 20 years, begging the question of whether these guidelines are scientifically informed and warranted.
Public concern about the short-term risk of cell phone exposure often stem from the health risks of nuclear radiation exposure, whose energy could ionize molecules and prompt uncontrolled cell division and cancer.  However, such risks in cell phone exposure have been roundly rejected: radio frequency radiation rarely has the ability to ionize cells since cell phone transmissions stray from the non- ionizing 3 kHZ to 300 GHZ frequency range.  Indeed, studies investigating whether radio frequency fields affect sleep, heart function, brain activity, and other bodily functions have found no definitive links between adverse health effects and radio frequency energies. 
High quality studies looking at longer exposures over multiple years, however, are few but critically necessary given the potential of chronic cell phone use to lead to tumors after many years of interaction. More recent studies have found both associations and non-associations between cell phone use and adverse health effects.
While a study in 2001 found no evidence that risks of brain tumors were higher among regular cell phone users of at least 5 years, heavy use in this paper was defined as 60 minutes or more per day, a measure that is outdated given how much smart phones have evolved and become such critical parts of our lives.  In 2007, an analysis of 16 case-control studies of at least 10-year cell phone users found a consistent pattern of increased risk for brain tumors, reporting that using cell phones for at least 10 years increased odds of acoustic neuroma and glioma, two different types of brain tumors, by 140% and 100%, respectively.  More recently, as the largest retrospective case-control study conducted by the International Agency for Research on Cancer, the Interphone study pooled analysis of data from 13 countries and found that while no increased risk of brain tumors were linked to mobile phone users of at least 10 years, odds of developing the glioma brain tumor increased by 40% for the heaviest 10% of cell phone users.  Importantly, the authors note that biases and errors prevent a causal interpretation and urge further research. 
Results that have been reported are inconclusive but raise red flags, urging increased research in the long term effects of cell phone radiation exposure. Indeed, children face especially high potential risks given the sensitivity of their developing brains, and the World Health Organization has pushed for further research in this population.  Given the recency of popular cell phone use among young people, and thus a potentially longer lifetime of exposure, research will be especially important in elucidating whether health risks are present and, if so, through what biological mechanisms. In the meantime, the California Department of Public Health is following the World Health Organizations International Agency for Research on Cancer lead in declaring mobile phone radiation as possibly carcinogenic to humans, perhaps rightfully so.
© Jason Li. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 R. Baan et al., "Carcinogenicity of Radiofrequency Electromagnetic Fields," Lancet Oncol. 12, 624 (2011).
 A. Macmillan, "Cell Phone Radiation May be Dangerous, California Health Officials Warn," Time, 18 Dec 17.
 A. Summerville, "Cell Phone Radiation vs Nuclear Radiation," Physics 241, Stanford University, Winter 2017.
 P. Inskip et al., "Cellular-Telephone Use and Brain Tumors," New Engl. J. Med. 334, 79 (2001)
 L. Hardell et al., "Long-Term Use of Cellular Phones and Brain Tumors: Increased Risk Associated With Use for ≥ 10 Years," Occup. Environ. Med. 64, 626 (2007)
 Interphone Study Group, "Brain Rumour Risk in Relation to Mobile Telephone Use: Results of the Interphone international Case-Control Study," Int. J. Epidemiol. 39, 675 (2010)