A recent large study by the US National Toxicology Program (NTP) exposed large groups of lab rats and mice to RF energy over their entire bodies for about 9 hours a day, starting before birth and continuing for up to 2 years (which is the equivalent of about 70 years for humans, according to NTP scientists). The study found an increased risk of tumors called malignant schwannomas of the heart in male rats exposed to RF radiation, as well as possible increased risks of certain types of tumors in the brain and adrenal glands. But some aspects of this study make it hard to know just how well these results might be applied to cell phone use in people. For example, there was no clear increased risk among female rats or among male or female mice in the study. The doses of RF radiation in the study were also generally higher than those used in cell phones (ranging from 1.5 W/kg to 6 W/kg in rats, and 2.5 W/kg to 10 W/kg in mice), the animals’ entire bodies were exposed, and the amount of time they were exposed was longer than most people typically spend on the phone each day. The male rats in the study exposed to RF waves also lived longer, on average, than the rats who were not exposed, for unclear reasons. Because of this, the NTP has noted that the study results cannot be directly applied to humans. Still, the results add to the evidence that cell phone signals might potentially impact human health.
Over time, the number of cell phone calls per day, the length of each call, and the amount of time people use cell phones have increased. Because of changes in cell phone technology and increases in the number of base stations for transmitting wireless signals, the exposure from cell phone use—power output—has changed, mostly lowered, in many regions of the United States (1).