Parents should think twice before giving in to a middle-schooler's demands for a cell phone, some scientists say, because potential long-term health risks remain unclear.

Researchers have speculated for more than 10 years that the electromagnetic radiation emitted from cell phones may damage DNA and cause benign brain tumors, said Henry Lai, a bioengineering professor at the University of Washington.

"We don't know very much about the health effects of cell phone use on kids, but there are speculations," Lai said.

In Britain, the chairman of the National Radiological Protection Board advised in January that parents should not give mobile phones to children age 8 or younger as a precaution against the potential harm of radiation from the devices.

When you use a cell phone, 70 to 80 percent of the energy emitted from the antenna is absorbed by the head, Lai said.

Last week, a federal appeals court in Maryland reinstated five class-action lawsuits claiming that the cell phone industry has failed to protect consumers from unsafe levels of radiation.

Several research studies have pointed to the potential impacts of long-term absorption of cell phone-emitted radiation but little of the research has focused on the children.

Lai said he was concerned about the impact on children because young skulls are thinner and the growing brain may be more susceptible to radiation.

He also said that because brain tumors usually take 30-40 years to develop, children who use cell phones from their teen years onward would have a longer period of time to see a cumulative impact.

"We don't know if kids are really more susceptible," Lai said, but he encourages everyone to use a headset to keep the antenna away from the brain, "even if they're not cool."

Most research on the subject has stopped in the United States except for some work supported by the cell phone industry, he added. Independent studies continue in Europe.

A Swedish study published in October suggested that people who use a cell phone for at least 10 years might increase their risk of developing a rare benign tumor along a nerve on the side of the head where they hold the phone.

The study's subjects had been using cell phones for at least 10 years, nearly all analog models that emit more electromagnetic radiation than the digital models now on the market.

Digital phones emit radiation in pulses; the older analog varieties emit continuous waves. Since cell phones exploded in popularity in the late 1990s, most of those sold used digital technology.