A warning from the head of a prominent cancer research institute has rekindled fears about the possible health risks associated with extensive cell-phone use, especially among children--and it comes as a growing number of children are using cell phones to communicate.

Dr. Ronald B. Herberman, director of the University of Pittsburgh Cancer Institute, issued an unprecedented warning to his faculty and staff on July 23: Limit cell-phone use because of the possible risk of cancer.

Herberman's warning is contrary to numerous studies that don't find a link between cancer and cell-phone use, as well as a public lack of worry by the U.S. Food and Drug Administration.

Herberman is basing his alarm on early, unpublished data. He says it takes too long to get answers from science, and he believes people should take action now--especially when it comes to children.

"At the heart of my concern is that we shouldn't wait for a definitive study to come out, but err on the side of being safe rather than sorry later," Herberman said.

No other major academic cancer research institutions have sounded such an alarm about cell-phone use. But Herberman's advice is sure to raise concern among many cell-phone users--especially parents and educators.

Nearly one out of every two tweens (kids between 10 and 13 years old) and 83 percent of teens in the United States now own a cell phone, according to new data from Chicago-based C&R Research.

In the memo Herberman sent to about 3,000 faculty and staff, he says children should use cell phones only for emergencies, because their brains are still developing.

Adults should keep the phone away from their head and use the speakerphone feature or a wireless headset, he says. He even warns against using cell phones in public places such as a bus, because this exposes others to the phone's electromagnetic fields.

The issue that concerns some scientists--though nowhere near a consensus--is electromagnetic radiation, especially its possible effects on children. It is not a major topic in conferences of brain specialists.

A 2008 University of Utah analysis looked at nine studies, including some that Herberman cites, with thousands of brain tumor patients and concludes: "We found no overall increased risk of brain tumors among cellular phone users. The potential elevated risk of brain tumors after long-term cellular phone use awaits confirmation by future studies."

Studies last year in France and Norway concluded the same thing.

"If there is a risk from these products--and at this point, we do not know that there is--it is probably very small," the Food and Drug Administration says on an agency web site.

Still, Herberman cites a "growing body of literature linking long-term cell-phone use to possible adverse health effects, including cancer."

"Although the evidence is still controversial, I am convinced that there are sufficient data to warrant issuing an advisory to share some precautionary advice on cell-phone use," he wrote in his July 23 memo.