Are airport x-ray scanners safe for passengers?

NPR : By the end of next year, one out of every six airline passengers at US airports will be asked to go through a scanner that uses backscattered x rays to find concealed weapons. In absolute terms, the radiation dose delivered to each passenger in one scan is tiny: 0.02 microsieverts, about 1/1000th of the dose the same passenger would receive from cosmic rays during a transcontinental flight. But, as NPR’s Richard Knox reported earlier this year, a group of biochemists and biophysicists from the University of California, San Francisco, has challenged the assumption that the scanners are safe, despite the low dose. The scientists question whether the prime safety criterion should be the overall dose, if, as they suspect, the dose is concentrated in the passenger’s skin.