Are cell phones bad for your health? With so many in use — nearly 90 million in the United States — this wouldn’t seem to be an open question. But it is. Researchers’ prevailing view is that there’s no proof yet that cell phones are hazardous, but they’re not ready to declare the devices safe.

The potential risk comes from the low-level radio-frequency radiation that mobile phones produce. When in use, cell phones send a microwave signal from the antenna to a base station, which can be miles away. The strength of the signal increases depending on the distance to the base station or if the phone is used inside a building or car. The angle at which the user holds the phone can also increase the exposure.

Researchers are searching for a link between the radio-frequency radiation and rates of brain cancers or damage to genetic material. None has produced definitive results. In one case, a recent study done in Great Britain urged parents to limit their children’s cell-phone use — not because it had confirmed a health risk, but because children would be more at risk because of their developing nervous systems. No kidding.

The $200 billion-a-year cell-phone industry likes to accentuate the positive. "The wireless industry’s position is that there’s been research done, but none of it has shown a conclusive link between the wireless phones and ill health," says Ellen Mullally, spokeswoman for the Alexandria-based Personal Communications Industry Association. Instead, she says, cell phones actually improve safety by giving people quick access to help. Data from her group claims that about a third of people get cell phones for safety reasons.

The cell-phone industry has funded its own research. In 1993 it began a five-year, $25 million study of health effects of cell phones. The research turned up no smoking gun but created a nasty public relations problem last October when the study’s director, George L. Carlo, blasted some segments of the industry for "repeatedly and falsely claiming that wireless phones are safe for all consumers" and failing to fully inform consumers. The Cellular Telephone Industry Association fired back, accusing Carlo of conflicting with his own earlier, less ominous comments about the research.

Soon after the spat between Carlo and the trade association, the U.S. Food and Drug Administration weighed in. The FDA didn’t say cell phones were safe, only that the "available scientific evidence" didn’t demonstrate a risk. Some experiments on laboratory animals suggested low levels of radiation could accelerate the development of cancer, but it’s not clear whether that applies to humans. If the phones are found to be a health risk, the FDA can order makers to repair or replace them. More studies are planned.