A mobile phone's main source of RF energy is its antenna, so the closer the antenna is to a phone user's head, the greater the person's expected exposure to RF energy.

Because RF energy from a cell phone falls off quickly as distance increases between a person and the radiation source, the safety of mobile phones with an antenna mounted away from the user — like on the outside of a car — has not been called into question. Also not in doubt is the safety of those so-called cordless phones that have a base unit attached to a home's telephone wiring and operate at much lower power levels than cell phones.

Many experts say that no matter how near the cell phone's antenna — even if it's right up against the skull — the six-tenths of a watt of power emitted couldn't possibly affect human health. They're probably right, says John E. Moulder, Ph.D., a cancer researcher and professor of radiation oncology at the Medical College of Wisconsin. It's true, he says, that from the physics standpoint, biological effects from mobile phones are "somewhere between impossible and implausible."

At the same time, Moulder supports further studies into the science of cell phone radiation. "Some people think the power emitted by the phones is so low, it's a silly thing to research. But I think it remains a legitimate area of study."

Cell Phone/Cancer Studies in Perspective
Some mobile phone users have been diagnosed with brain cancer, and many others who have not used mobile phones have gotten the disease, too. Each year in the United States, brain cancer occurs at a rate of about six new cases per 100,000 people. Among the 100 million Americans who own mobile phones, then, about 6,000 cases of brain cancer would be expected among them in a year, even if they had not used mobile phones.

Scientific studies have focused on the question of whether the statistical risk of getting brain cancer is increased in those who use mobile phones compared to non-users, leaving to the courts the judgment of whether Chris Newman or other individuals would have gotten the disease had they not used a cell phone.

Two types of studies are generally used to investigate suspected cancer causes: epidemiological studies, which look at the incidence of a disease in certain groups of people, and animal studies.

Epidemiological studies are sometimes difficult to carry out in a way that can determine whether a cause-and-effect relationship exists between a single variable in a person's life (in this case, cell phone use) and the person's disease (brain cancer). Some factors that complicate research into the asserted link between cell phones and brain cancer: Brain cancer can take years or even decades to develop, making possible long-term effects of mobile phone use difficult to study; mobile phone technology is ever-evolving; and so many lifestyle factors — even down to the precise position in which a person holds the phone, as well as his or her own anatomy — can affect the extent of radiation exposure.

Studies in animals are easier to control, but entail complications of their own. For example, how should results obtained in rats and mice be interpreted in terms of human health risks? And how can scientists account for the fact that these studies sometimes expose animals to RF almost continuously — up to 22 hours a day — and to whole-body radiation, unlike people's head-only exposure?

While studies generally have shown no link between cell phones and brain cancer, there is some conflicting scientific evidence that may be worth additional study, according to the FDA.

Based on the evidence so far and possible limitations in some studies' research methods, the FDA is closely following ongoing research into whether there might be any association between cell phones and cancer, according to the agency's Feigal.