However, a few scientists worry that machines might malfunction, raising the risk of cancer.
The Transportation Security Administration says radiation from one scan is about the same as a person would get from flying for about three minutes in an airplane at 30,000 feet, where atmospheric radiation levels are higher than on the ground.
That amount is greatly lower than a single dental X-ray.
"We are confident that full-body X-ray security products and practices do not pose a significant risk to the public health," officials from the Food and Drug Administration and the TSA wrote in a letter last month to White House science adviser John Holdren.
But concern has surfaced among some passengers fearful about excess radiation, flight crews already overexposed to in-air radiation and even a few scientists.
"The thing that worries me the most is what happens if the thing fails in some way" and emits too much radiation, said Arizona State University physics professor Peter Rez.
The Associated Press Contributed to this report.