) -- Scientists who testified at this week's Senate


"The Health Effects of Cell Phone Use" agreed on one basic idea: Until they can prove it's not bad to hold a cell phone to your face, you ought to take precautions.

At the Washington hearing, U.S. Sen. Tom Harkin (D-Iowa) asked each of the panelists whether they would recommend using a headset with a mobile phone. Most said doing so would keep the phone from zapping radio frequency, or RF, waves directly into your face. An Israeli study from 2007 found that frequent cell-phone users had a higher level of salivary gland tumors.

The safest bet is a wired headset, many of the panelists said. Though a Bluetooth headset usually emits lower RF levels than a cell phone, a wired headset, while less comfortable, doesn't give off any radio waves.

The scientists also confirmed at the hearing that the level of RF radiation from cell phones fluctuates depending on location. For example, phones emit the highest levels of RF in areas such as moving trains and elevators, when they're working harder to find a signal.

Panelist Siegal Sadetski, an epidemiologist in Tel Aviv, said her 2007 study found a higher level of salivary gland tumors among rural cell-phone users. In rural areas, cell phones must emit stronger signals to find a base station. The same study found a significant increase in salivary gland tumors among frequent cell-phone users, and the tumors corresponded with the side of the face that they usually held their cell phones. But she wouldn't go as far to say that cell phones cause cancer because the study included only a few thousand people. "The fact that all these indications appeared where they should have appeared told me that there was a red light, but as a scientist there's not enough to conclude causality," she said.

Linda Erdreich, a consultant hired by the wireless telecom advocacy group


and the sole industry representative on the panel, said: "I recognize the use of an earphone would decrease the exposure to RF, but I can't agree that it reduces the risk because I don't think the total picture suggests that there


a risk from using cell phones."

"What comes through to me is that we just don't know what the answer is," said U.S. Sen. Arlen Specter (D-Penn.). "And precautions are not a bad idea."

The entire hearing can be seen