It is well known here that I'm no fan of the MMW or of the NoS in any form: it is expensive, ineffective (misses things a metal detector would find), invasive (particularly for people with medical devices or other innocent items under their clothes) and slow. It prevents passengers from maintaining sight of their belongings, increasing the risk of theft by security staff or other passengers.

However, this is not true:
There was one (1) paper about terahertz waves at a much higher frequency and enormously higher power level than used by MMW scanners. It provided a computer model (not measurements) that suggested (not proved) that there was a possible (not proven) mechanism which might (or might not) cause some type of damage to DNA strands. The technology described in the paper was significantly different from a MMW scanner, and even then, the author himself was very cautious about drawing any solid conclusions. The media, however, reported it as "airport scanners will shred your DNA."

There was a second paper casting doubt on even the tentative conclusions of the first paper.