Terahertz frequencies vibrate at the same frequency as normal bodily cells, therefore it boosts your immune system, increases the metabolic activity in the cells, increases cellular oxygenation, as well as increases blood flow.
When terahertz frequency penetrates the body, they pass through healthy cells at normal temperatures. However, when they pass through unhealthy cells, they cause them to vibrate faster, thus increasing their cellular temperature, and ultimately destroying the damaged cells in the process.