Dr. Ronald Herberman, director of the University of Pittsburgh Cancer Institute, and Dr. David Carpenter, director of Institute for Health and the Environment at University of Albany testified on cell phones before the House Subcommittee on Domestic Policy.

Herberman used a model to show radiation from cell phones would penetrate far deeper into a 5-year-old's brain than an adult's, CNN reported.

However, Dr. Robert Hoover of the National Cancer Institute said the incidence of brain cancer in children has not increased significantly from the late 1980s to 2005, the period during which cell phones became popular.

Studies have indicated that long-term cell phone use may be associated with brain cancer, Herberman told the committee.

"I cannot tell this committee that cell phones are definitely dangerous," Herberman said. "But, I certainly cannot tell you that they are safe."

Studies show cell phone radio frequency energy does cause "biological effects" without heating tissue, although not all of those effects are harmful, Carpenter said.