**1. Introduction**

#### **1.1 RF treatment effect**

The method of operation for the vast majority of esthetic energy-based devices (EBD's) is through the generation of heat causing physiologic modifications to the human tissue. RF energy is a method to deliver heat into the human body at a level and distribution required for the specific application. For sub-necrotic thermal applications, this heat can be a relatively low temperature for fibroblast stimulation and metabolism acceleration (hands free RF devices). Alternatively, the heat can be more aggressive, ablative coagulative and necrotic in nature (RF assisted lipolysis or Fractional microneedling technology). It may occur that during the same treatment, RF energy effects will be both non-ablative on the skin and ablative-coagulative sub-dermally.

In most instances with RF, microwave and light-based technologies, heat is the result of a common pathway for the desired thermal effects. This understanding has given rise to an entire generic category of esthetic and medical EBD's*.* A variety of technologies and devices have been developed based on thermal treatment of tissue, either ablative or non-ablative, selective, or non-selective, using optical energy, RF electrical current, focused ultrasound to generate the heat. The common outcome of these devices leads to some heat-assisted transformation of local tissue. This thermally stimulated tissue alteration or remodeling typically results from:

• Selective thermal targeting of tissue by focusing energy at the desired spot internally or externally. Energy can be delivered to the selected volume in a minimally invasive manner by focusing energy to penetrate the tissue under the skin surface. An example of a minimally invasive treatment is electro-surgical devices which deliver thermal energy into the body via a tiny cannula or needle. Alternatively, electrocautery devices focus the energy on the tissue surface, ablating the tissue in proximity of the tip of the instrument to dissect the a soft tissue.

• Non-selective bulk heating, used mostly for sub-necrotic heating to stimulate natural processes in the body leading to increased production of collagen, elastin and ground substances. The result may include tissue tightening, circumferential reduction and wrinkle reduction.

RF energy is an important part of the armamentarium for treatment options comprising tissue cutting and coagulation, minimally invasive selective tissue targeting and bulk heating. RF current is the accepted type of energy used in four out of five surgeries conducted in the world and most industry leaders in the aesthetic field employ RF energy in at least one of their applications.
