Scientists are currently split on the level of danger the biological effects of the magnetic field emitted by cellular telephones poses to humans.
However, society "must not repeat the situation we had with the relationship between smoking and lung cancer where we ... waited until every 'i' was dotted and 't' was crossed before warnings were issued," said David Carpenter, director of the Institute of Health and Environment at the University of Albany, in testimony before a subcommittee of the US House of Representatives Committee on Oversight and Reform.
"Precaution is warranted even in the absence of absolutely final evidence concerning the magnitude of the risk" -- especially for children, said Carpenter.
Ronald Herberman, director of the University of Pittsburgh Cancer Institute -- one of the top US cancer research centers -- said that most studies "claiming that there is no link between cell phones and brain tumors are outdated, had methodological concerns and did not include sufficient numbers of long-term cell phone users."
Many studies denying a link defined regular cell phone use as "once a week," he said.
"Recalling the 70 years that it took to remove lead from paint and gasoline and the 50 years that it took to convincingly establish the link between smoking and lung cancer, I argue that we must learn from our past to do a better job of interpreting evidence of potential risk," said Herberman.
A brain tumor can take dozens of years to develop, the scientists said.
Carpenter and Herberman both told the committee the brain cancer risk from cell phone use is far greater for children than for adults.
Herberman held up a model for lawmakers showing how radiation from a cell phone penetrates far deeper into the brain of a five-year-old than that of an adult.
The committee were shown several European studies, particularly surveys from Scandinavia -- where the cell phone was first developed -- which show that the radiation emitted by cell phones have definite biological consequences.
For example, a 2008 study by Swedish cancer specialist Lennart Hardell found that frequent cell phone users are twice as likely to develop a benign tumor on the auditory nerves of the ear most used with the handset, compared to the other ear.
A separate study in Israel determined that heavy cell phone users had a 50 percent increased likelihood in developing a salivary gland tumor.
In addition, a paper published this month by the Royal Society in London found that adolescents who start using cell phones before the age of 20 were five times more likely to develop brain cancer at the age of 29 than those who didn't use a cell phone.
"It's only on the side of the head where you use the cell phone," Carpenter said.
"Every child is using cell phones all of the time, and there are three billion cell phone users in the world," said Herberman.
He added that, like the messages that warn of health risks on cigarette packs, cell phones "need a precautionary message."
Carpenter described the situation as "a critical public health issue," and called on the US government to support further research and for the Federal Communications Commission (FCC), in charge of monitoring the use of the radio spectrum, "to review their standards."
Also testifying was Julius Knapp, who heads the FCC office of engineering and technology -- responsible for setting limits for human exposure to radio frequency (RF) energy from electronic devices like telephones that they approve, to prevent it from heating up live tissue.
"It is important to understand that we rely on guidance from US health, safety and environmental agencies in setting those limits," Knapp said.
He added: "The FCC staff is not sufficiently qualified to speak with authority to the science of health effects of RF absorption in the body."