There's still a difference between the kind of radiation exposure that occurs during a flight compared to during a screening. My understanding is that radiation exposure during a flight is due to cosmic rays which are equally likely to cause damage throughout the body. The X-rays used by the TSA are at lower energy and are deposited almost exclusively in the skin. Since the volume of skin is much less than the total volume of your body, the radiation dose that your skin is receiving from the TSA is much larger than the dose during a flight.
While I'm very glad they're no longer in use in airports, I never saw a satisfactory answer to this. Perhaps I misunderstand the physics here, but wouldn't 10µrem across 100% of tissue be equivalent to, for instance, 1,000µrem across 1% of tissue?
Yes, that's correct. However, the difference in damage that that will do is still not clear. It's possible that skin tissue is more susceptible to damage than other kinds of tissue. (Or perhaps it's less susceptible.) Moreover, low-energy X-rays may do different kinds of damage than relatively high-energy X-rays or cosmic rays. Just looking at rem ignores a lot of variables about the long-term biological effects of the ionizing radiation.
