Back when the before X-rays were well understood, they were treated like 'wonder rays' that could never be harmful and could maybe even heal you. Now we know better and thoroughly test what damage other forms of radiation can do to our bodies. This includes terahertz radiation, which has great potential and now its effects on DNA have been studied, as reported by the Optical Society of America.
Terahertz radiation exists between microwaves and infrared light, and like microwaves interact strongly with water. These interactions are actually so strong that less energy is need to cause an observable effect, so, in theory, they would be safe to use to probe under the skin. That theory has now been tested and while in one sense it has failed, in another sense it may have succeeded. Though the terahertz photons do not have the energy to break bonds within DNA, they can cause a vibration in the molecule that can damage it. Eventually this damage could lead to cancer, but the researchers also noticed cells responding to the damage molecule, in order to repair or destroy it.
While the prospect of terahertz radiation causing cancer may seem like a reason to leave it alone, this apparent ability to enable our bodies' defenses to cancer could enable new kinds of treatments. Only more research will tell us that though; a lot more research.
Source: Optical Society of America