The head of the Federal Communications Commission is asking for a review of the agency's stance on radiofrequency energy emitted from cell phones amid lingering concerns that the devices may cause brain tumors.

FCC Chairman Julius Genachowski on Friday circulated a proposal to his fellow commissioners calling for a formal inquiry into the mobile phone emissions standards set in 1996.

The proposal would need to be approved by a majority of the FCC's five commissioners before the agency could release it for public comment. If it is approved, the agency would consider changing its testing procedures and seek input on the need to either strengthen or ease the current standards.

The agency would also look into whether emission standards should be different for devices used by children, an FCC spokesman said on Saturday.

The spokesman stressed that the agency continues to believe there is no evidence tying cancer, headaches, dizziness, memory loss or other health problems to mobile phones.

But the inquiry would seek any scientific evidence that could warrant changes to the emissions standards.

The number of mobile phones has risen sharply since the early 1980s, with nearly 5 billion handsets in use today, prompting lengthy debate about their potential link to the main types of brain tumor, glioma and meningioma.

In May 2011 the World Health Organization added cell phone radiation to a list of possible carcinogens, putting it in the same category as lead, chloroform and coffee, and said more study is needed.

Unlike ionizing radiation such as that from gamma rays, radon and X-rays, which can break chemical bonds in the body and are known to cause cancer, radiofrequency devices such as cell phones and microwaves emit radiofrequency energy, a form of non-ionizing radiation.

According to the National Cancer Institute, there is no consistent evidence that non-ionizing radiation increases the risk of cancer.

STUDIES POINT AWAY FROM LINK

What these devices do produce is energy in the form of heat, and the concern is that frequent use of cell phones held up to the ear can change brain cell activity, as some studies have suggested.

What is not yet clear is whether this causes harm, which is why the WHO and other health bodies have called for further study.

But since the WHO's announcement, scientific evidence has increasingly pointed away from a link between mobile phone use and brain tumors, according to a panel of the International Commission on Non-Ionizing Radiation Protection.

Last October a study by Danish researchers involving more than 350,000 people concluded that mobile phones do not increase the risk of cancer, concurring with other studies that have reached similar conclusions.

And a study last July looking at children and adolescents aged 7 to 19 concluded that those who used mobile phones were at no greater risk of developing brain cancer than those who did not use the devices.

The FCC in 1996 established a limit on emissions and a safe level of human exposure. Mobile phones are tested and must be within this limit before they are granted FCC approval to be marketed in the United States.

FCC spokeswoman Tammy Sun said that the existing guidelines do not pose any harm or risk to cell phone users, adding that the United States "has the most conservative emissions standards in the world."

"Our action today is a routine review of our standards," Sun said in a statement.

The FCC does not set health policy, relying instead on input from the Food and Drug Administration, Department of Health and Human Services and other agencies.

"We hope and expect that other federal agencies and organizations with whom we work on this issue will participate in the process," Sun said.

Demand for wireless devices like Apple Inc's iPhone and Google Inc's suite of Android-powered smartphones has surged in recent years, with some consumers opting to forgo landline service altogether.

According to a study by Cisco Systems Inc, the number of mobile devices connected to the Internet is expected to exceed the number of people on Earth in four years' time.

For people who are concerned about the effects of radiofrequency energy from cell phones, the FDA and FCC suggest they have shorter conversations on them and use a hands-free device, which places more distance between the phone and the user's head.