Dear Science,

I decided to follow your advice and opt out of the scanner in favor of a pat-down. The TSA agent seemed very annoyed and at first tried to dissuade me by making the pat-down seem very invasive and embarrassing. Then she asked me why I was refusing to go through the scanner. I told her I had concerns about the radiation, to which she replied that if that was my concern then I probably shouldn't be flying. Nice. She spouted the line about it being equivalent to only two to three minutes of flight radiation and finally gave up. I had to wait approximately five minutes for an agent to get around to doing the pat-down.

Was the agent right? What does the radiation do to the body?


The TSA agent, quoting the manufacturer of these scanners, is correct with regard to the most common way we measure radiation exposure—in terms of energy delivered per kilogram of stuff. This way of thinking goes back to the 1950s and the dawn of the atomic era, before we really understood DNA and why this sort of radiation is dangerous to living things.

In each of our cells is 46 chromosomes' worth of DNA holding all of our genetic material, contained in 23 pairs. Each chromosome is made up of an unbroken double strand of DNA—a delicate chain merely two atoms wide, but hundreds of millions of atoms long. Ionizing radiation—like X-rays—cuts these strands into two pieces. To repair this damage—something incredibly important, given the volume of cosmic radiation we're exposed to—our cells have two techniques. One is to use the fact that our chromosomes are paired. The flailing ends of the broken strand are paired up with their sister chromosome, the damaged area cut out and replaced with the good copy from the sister. This is a high-quality repair, but it takes time and significant effort on the part of the cell. When overwhelmed, cells instead take the loose ends of cut DNA, nibble down the frayed bits, and then shove the ends back together again. The nibbling step is dangerously mutagenic.

Cosmic radiation—like you get exposed to while flying for a few minutes—comes in high-energy photons; the total dose of energy comes in a few intense bursts. The damage is done, but over time and in a way that our cells have a good chance to complete a high-quality repair. These scanners, in contrast, emit a showering of lower energy X-ray photons—a similar amount of total energy, but spread out over a lot more photons. While lower energy, the X-rays used are still capable of causing double-strand breaks in DNA. It's not clear yet if these more numerous cuts can be still repaired by high-quality means. Just one of many reasons why I (and others) think the safety of these scanners is not quite settled.

Irradiatingly Yours,


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