Avoiding unnecessary radiation is part of an Age Management Medicine program.

When you are in the airport the next time, you may notice these full body scanners and you may be asked to use one during the security process.

The machines emit X-ray energy levels that would be safe if they were distributed throughout the body, but a majority of that energy is delivered to the skin and underlying tissue at levels that "may be dangerously high," the researchers wrote last month to the White House Office of Science and Technology.

Two Rapiscan backscatter machines have been tested over the past two years at Los Angeles International Airport, with more expected to arrive by the end of the year as part of a nationwide deployment.

This technology is also being used at Atlanta- Hartsfield-Jackson airport.

"These scanners work because of the energy level of X-rays being concentrated on one area of the body," said David Agard, a professor of biochemistry and biophysics at UC San Francisco and one of the four researchers who raised concerns about the machines.

"The numbers are small, mind you, so it's not like this is a chest X-ray by any means," Agard said. "But it is an increment of radiation that isn't trivial."

With radiation, cumulative exposure increases your risk for cancer.

If you travel often, you don't want to expose yourself repeatedly.

Officials with the Department of Homeland Security defended the use of Rapiscan's backscatter machines, which are 9 feet long and 6" feet wide and bounce low-level X-rays off airlines passengers to peek underneath clothes as a secondary security screening measure.

While radiation exposure should be avoided, the amount of energy emitted from the machines is equal to two minutes in flight at cruising altitude, said Dr. Alex Garza, chief medical officer for the Department of Homeland Security.

Travelers who do not wish to be screened can still opt for a full-body pat-down, Garza said.

The Transportation Security Administration is expected to install 450 backscatter machines at LAX and 10 other airports across the country by the end of the year, funded by the American Recovery and Reinvestment Act.

At a cost of $190,000 each, the scanners produce intimate images that obscure the faces of passengers, but natural curves and crevices are seen clearly enough to detect hidden weapons or explosives.

The graphic portraits are immediately deleted after they are viewed by security screeners in a remote, enclosed area away from passengers.

The National Council on Radiation Protection and Measurements released a statement last week that said a traveler would need to go through 2,500 body scans annually -- or 10 times a day for a year -- to meet the annual effective dose.

Researchers at UC San Francisco said that comparing the X-ray levels emitted from the machines to cosmic ray exposure during flights is "misleading."

"Air travel cosmic rays are understood in terms of whole body volume doses, while these airport scanners deposit their energy directly into the skin," Agard said. "We're not trying to be alarmist, but cautious, and we would like the government to test these machines before they are put into wide use."

Officials with the U.S. Food and Drug Administration said they found no problems with Rapiscan's backscatter machines during tests conducted with the National Institute of Standards Technology and the Johns Hopkins University Applied Physics Laboratory.

The FDA is expected to respond to concerns raised by the team of UC San Francisco researchers sometime next month.

"We took their question seriously, but these machines are safe for the general public, including sensitive groups cited by UC San Francisco," said Daniel Kassiday, an FDA specialist in radiation hazards. "The risk levels are extremely low, but communicating risk is never an easy thing when it comes to radiation."

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