Emerging THz technological applications
THz waves are found between microwaves and infrared on the electromagnetic spectrum. This type of radiation was chosen for security devices because it can penetrate matter such as clothing, wood, paper and other porous material that's non-conducting.
This type of radiation seems less threatening because it doesn't penetrate deeply into the body and is believed to be harmless to both people and animals.
THz waves may have applications beyond security devices. Research has been done to determine the feasibility of using the radiation to detect tumors underneath the skin and for analyzing the chemical properties of various materials and compounds. The potential marketplace for THz driven technological applications may generate many billions of dollars in revenue.
Because of the potential profits, intense research on THz waves and applications has mushroomed over the last decade.
Source (more about health risks)