Airline passengers will face the long lines, interminable delays and frustrating backups that come with holiday travel. Through it all, they’ll also have to decide whether to submit to one of the 500-plus x-ray or radio wave scanners found in airports nationwide and wonder about their safety.

Much of the debate surrounding the increasingly common security scanners revolves around their effectiveness and privacy. But the health implications are coming to the fore as the European Union bans x-ray scanners because of health concerns. Many EU nations will instead use millimeter-wave, lower...