Devices such as these use a form of electromagnetic energy called radio frequency energy, which consists of waves of electric and magnetic energy moving through space. The radiation that comes from these devices is different from and much less than the radiation that comes from X-rays.
Still, researchers and environmental watchdogs have speculated that increasing exposure to these devices, such as holding a cell phone close to your head for extended periods of time, may expose you to harmful levels of radio frequency energy. There have been reports of associations between heavy cell phone use and certain types of brain tumors, for example, but the evidence is inconclusive.
There have also been suggested links between heavy maternal cell phone use during pregnancy and impaired fetal brain development, as well as later concerns about behavior problems. Other studies have examined links between radiofrequency exposure, such as living close to a cell phone tower, and pregnancy problems. There's no scientific evidence to support such an association. For now, evidence indicates no cause for alarm. Still, if you're concerned about your exposure to radio frequency energy, you might consider making fewer cell phone calls or using a hands-free head set to make your calls.