[nitrogen]

Millimeter waves are not ionizing, while the x-rays used by TSA backscatter machines and medical x-rays are.

[dredmorbius]

The question isn't whether or not they're ionizing. The question is whether or not they have adverse biological actions.

[noonespecial]

Its highly likely that those are in fact the same question.

[dredmorbius]

Not when asked by me.

http://scholar.google.com/scholar?q=physiological+effects+of...

My general sense: any health effects are likely to be weak at levels typically encountered, but I'm holding as plausible that thee may be some effects.

[aortega]

Microwave oven radio waves are non-ionizing 2.4 Ghz and I suspect they cause several health issues to any living organism exposed to them, even for a short time.

[lawnchair_larry]

They aren't, unless you're in the oven. And that's different.

[dredmorbius]

For some people, there's a risk on the outside as well. Pacemakers.

Less so these days, but still.

My understanding is that there's a possibility of creating induced current in the pacemaker. Which is to say, the non-ionizing radiation has an effect at a distance, albeit in a manufactured artifact, not (in this case) organic tissue.