There are two types of high frequency treatments: a Direct High Frequency facial uses a gas-filled glass electrode passed over gauze placed on the skin. The gas housed inside of the electrode is either Argon gas, also called the Tesla current and the violet ray for its purple color, or Neon gas, which is orange. The violet ray is for acneic skin. 

Once the gas ignites, light energy is given off, it reacts to the oxygen around the electrode which creates ozone. Ozone kills bacteria. The violet ray is for acneic skin. It helps to dry out the follicle and has an antibacterial effect to kill the P acnes bacteria, so it is good for oilier, blemish-prone skin. An indirect high frequency, also called Viennese massage facial uses a saturator, or electrode held by the client to draw a moisturizing massage medium deeper i to the skin as the esthetician uses light, effleurage movements over the face, and so it is best suited for more mature or dry skin types.