The booth-type body scanners common at airports around the world are millimetre-wave scanners that use ultra-high frequency millimetre wave radiation rather than X-rays.
These have wavelengths in the range of 1-10 millimetres, which is much larger than those emitted by an X-ray machine and have less impact on small structures such as human proteins and nucleic acids, and there is no proven health risk.
Some US airports use backscatter X-ray scanners which emit between 0.03 microsievert and 0.1 microsievert of radiation.
Although this is ionising radiation with the potential to cause cancer, the dose is tiny compared to other sources of radiation.
We are exposed to about 2.4 millisieverts of natural background radiation annually, more than 20,000 times more than the maximum radiation dose from a backscatter scan.
One hour in a jet aircraft at cruise altitude exposes your body to around five microsieverts per hour, at least 100 times more than that from a single scan from a backscatter X-ray.
The rectangular gate that you pass through as part of the airport security scan is an electromagnetic field device which reacts to metal objects and has no proven health risk.