Cell phones can be a life-saver. Can they be a life-shortener, too? Every technological leap brings fears about health risks, but harmful influences can take decades to cause disease. So what can we say now about the portable phones?

Cell phone antennas use high frequency electromagnetic waves to communicate with base stations. The radiation emitted at these frequencies can't break chemical bonds in your body's cells, but there could be other biological effects. Some researchers are concerned because cell phone antennas concentrate their energy in a very small region against the head. If this is indeed a problem, children are at highest risk because they have thinner skulls than adults—and these days often have phones of their own.

One study in the Annals of Neurology found that cell phones affect the brain's electrical activity. Fifteen young men were exposed to cell phones that were turned either on or off. When the phones were on, neurons on the near side of their brain were slightly more active. The effect lasted for at least an hour.

Team leader Paulo Rossini of the University of Rome says the study showed "an influence of mobile phone emissions on the cortex, the most delicate and sophisticated part of the brain," but no one can yet tell whether the effect is harmful, neutral, or even beneficial. (It's theoretically risky for those with epilepsy, because seizures can be triggered more easily when the brain is electrically excited.) Previous studies have looked at how mobiles affect brain functions like attention. Some found positive effects, while others found negative effects or none at all. For example, Australian scientists discovered in last year that cell phone use can temporarily help you with certain tasks that require working memory, but can also slow reaction time.

The biggest concern among the general public is that the phones could cause brain cancer. Except for one Swedish group's research, large epidemiological studies have found no connection. But Kjell Mild, professor of biology at the Swedish National Institute for Working Life, blames most researchers for not including enough long-term users. "If you look at the studies with large numbers of people who used mobiles for 10 years or more, all show an increased risk," he says.

John Moulder, professor of radiation oncology at the Medical College of Wisconsin, who has reviewed the mobile data, disagrees. He says there is no evidence that they cause brain cancer and "no real reason to expect them to." The FDA, which agrees that there is no evidence of phone-related health risks, states on its Web site that the Swedish group's data are "difficult to interpret."