The scanners use ionizing radiation, which could damage DNA. Early studies suggest that they are likely to trigger a small number of cancers every year from the millions of air passengers scanned.
The scanners, which detect explosives by revealing the full body underneath clothes, are already being used in hundreds of airports around the US. Eventually, every airport in the country will be equipped with them, says the US Transportation Security Administration.
European airports will instead be introducing body scanners that use radio frequency waves, believed to be a safer alternative, that still detect explosives being carried onboard.
A trial for the x-ray scanners is still taking place at some airports in the UK. After the trial is finished, they will be used only as a secondary security measure if the conventional metal detector picks up something suspicious.