U.S. regulators should take a fresh look at 15-year-old standards on radiofrequency energy from mobile phones, an investigative arm of the U.S. Congress said on Tuesday amid lingering concerns the devices may cause brain tumors.

Before a mobile phone comes on the U.S. market, it is first tested to ensure its emissions are within a limit determined by the Federal Communications Commission to be safe for human exposure.

But that limit may not reflect the latest research, and testing may not reflect the actual conditions under which mobile phones are used, such as when stored directly against the body in a pocket while someone talks through an ear piece, according to a Government Accountability Office report.

The report concludes a year-long investigation prompted by Democratic Representatives Edward Markey, Henry Waxman and Anna Eshoo.

"While the GAO report indicates there is no evidence to suggest using a cell phone causes cancer, it's important that safety standards are current and account for changing trends in cell phone use and technology," Eshoo said.

The GAO recommended that the FCC conduct a formal reassessment of its emissions limit and testing requirements and change them if appropriate.

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

If it is approved by a majority of the FCC's five commissioners, the agency would consider changing its testing procedures and seek input on the need either to strengthen or ease the current standards. The proposal also considers whether emission standards should be different for devices used by children.

The FCC would solicit input from a variety of experts, including federal health agencies, and take the GAO's report into consideration as part of its review, FCC spokesman Neil Grace said.

The agency has stressed that it believes there is no evidence tying cancer, headaches, dizziness, memory loss or other health problems to mobile phones.

NO CONSISTENT EVIDENCE OF LINK

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 forego landline phone service altogether.

The sharp increase in mobile phone usage has fueled lengthy debate about the 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.

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.

The wireless trade association, CTIA, noted that two decades of scientific research, evaluated by government agencies and impartial health organizations, have yet to establish that wireless phone use causes adverse health effects.

"The FCC's safety standards include a 50-fold safety factor and, as the FCC has noted, are the most conservative in the world," John Walls, CTIA's vice president of public affairs, said.

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