As the interest and demands for cosmetic treatments increase, the tendency of the rejuvenation treatment, which mainly depended on the surgical treatments in the past, is shifting toward less invasive, more effective treatments which allow faster recovery to normal lives. In line with such a tendency, the radiofrequency (RF) treatment is gaining more attention these days. Unlike the laser treatment, the RF treatment uses a new, nonablative technology utilizing electric current for skin rejuvenation. RF gives focal dermal heat damages on the dermis, which results in less damage on the epidermis, reduction in the adverse events, and faster recovery to normal lives. There is a variety of RF technology devices, including monopolar, bipolar, and factional RFs. In this review, we will summarize and compare the most representative studies in the field of RF technology.

RF energy has been in use with various medical devices. Bovies, which are still widely used in the operation rooms, are one of the most profound examples of RF electrocautery device. In dermatology, RF technology was first introduced for nonablative skin rejuvenation after FDA approved RF treatment for facial wrinkle reductions in early 2000s. And then RF devices were approved for off-face treatments in 2006.1

RF devices generate an electric current within an electromagnetic field of 3 kHz-300 mHz frequency.1–3 Once the current reaches the tissue, the current meet the unique resistance of the tissue, which is called the impedance. When the current goes through a tissue with electric resistance, heat is generated, as the electric energy is converted to heat energy.4 Such an energy discharge amount can be calculated using the following formula;

Here, I = current, z = impedance, t = time (seconds).

Therefore, it could be said that the amount of the generated energy depends on the energy that flows on the impedance of the target tissue. The subcutaneous fat layer or other places of high resistance can generate a larger amount of energy, thus making it possible for the heat to penetrate even deeper layers. While diffraction, absorption, and scatters cause the loss of a part of energy generated by a laser or other optical devices, RF energy is free from the influence of diffraction, absorption by the chromophores, or other tissue interactions, which, therefore, give no influences on to the epidermal melanin. For this reason it could be used for any skin types, and it is possible to control the depth of the energy’s infiltration.2–4

The contraindications of RF treatment include the patients with implantable medical devices, such as a pacemaker or a defibrillator. Those with collagen vascular diseases or autoimmune diseases are also contraindicated. In addition, caution is required when using RF treatments for patients who are under radioactive treatment or recurring herpes infections.5,6

RF devices come in two different types according to the configurations of electrode, which are the monopolar type and the bipolar type. The monopolar type uses a single electrode tip, which delivers energy to the space between the electrode and the grounding plate. The bipolar type passes electrical current between the two electrodes applied to the skin. The bipolar type penetrates a smaller volume of tissues, and this allows it to work even less energy compared to the monopolar type. The depth of heating depends on the size and geometry of the treatment tip. For the bipolar type, the depth is half of the distance between the two electrodes. This gives the monopolar type of being able to penetrate deeper, but the bipolar type is still superior in terms of the pain it causes.

One of the most representative devices of the monopolar type, the Thermacool system (Thermacool, Thermage, Inc., Hayward, CA) emits an RF energy of 6 MHz, which is delivered onto the skin through a disposable electrode tip. For this type of devices, cryogen is used as the cooling module. Fitzpartrick et al.7 conducted a large-scale clinical study using the monopolar RF technology and proved its efficacy in treating the periorbital wrinkles. In that study, 86 subjects were treated once with the device, and 83.2% of the treated patients showed grade 1 or higher improvement of the periorbital wrinkles. In addition, 61.5% of the patients showed an eyebrow lift of 0.5 mm or higher in a photographic assessment. As a result of this study, US FDA approved the use of Thermage on the upper face wrinkles in 2002, and the entire face in 2004.

In addition to facial rejuvenation, it could be used for improvement of the acne or acne scars. The most representative treatment mechanism of this technology for these conditions can be the restoration of the activities of sebaceous glands and the recovery of collagen in the dermis. In a clinical study with 22 patients, where 1 to 3 treatment sessions were given to the patients using 65–103 J/cm² of energy, 92% of the patients showed 75% or more reduction of the number of acne lesions, while 9% of them showed 25–50% reduction in lesion counts. In addition to the lesions of acnes, some patients also showed improvements of the acne scars.8

The treatment mechanism of the monopolar RF is to generate heat to cause two different effects on collagen. Firstly, the heat disintegrates the hydrogen bonds to change the triple helix structures, resulting in a contraction of collagen. Secondly, the gradual contraction along with wound healing process causes regeneration of collagen. Such changes take place of a period of 2 to 6 months in a slow pace, resulting in a thicker layer of regenerated dermis.9,10

Two aspects should be considered when determining which is better between treating in a single session with a higher energy or using less energy over a number of sessions. The first aspect is the ‘effect’, and the other is the ‘side effect’ of the treatment. In earlier days, using a higher amount of energy concentrated in a single session was more popular. The biggest problem with this approach was the pain it caused. Further studies afterwards revealed that applying a lower amount of energy over a number of sessions was more helpful for collagen denaturation and the improvement of the skin elasticity. Since then, bigger tips started to be used for the treatment, and the recent trend seems to apply less energy over a number of sessions.10

According to the studies of long-term treatment effects of the monopolar RF technology by Suh et al.,11 in which 8 patients were followed-up for a period of 6 to 7 years, they received 4 sessions of the treatment in average without using any other rejuvenation treatments. The severity of the wrinkles, based on Glogau’s wrinkle classification system, maintained the improved status without worsening after treatment. 75% of the patients were satisfied with the results, and 25% of the patients were highly satisfied. In the preceding studies, the patients in their 30s to 40s appeared to maintain the best effects, and the maintained effects reduced as the patients grew older. However, in the long-term follow-up study, patients of all ages, including those in their 60s, maintained the effects of the treatment desirably.11,12

The authors of the study concluded that, in consideration of the preceding findings that lower-energy/high passes approach was better in terms of the effects of the treatment and the stability of the patients, recommended multiple treatment sessions with approximately 1 year intervals and a higher number of passes in each session.11

The most representative of such studies are summarized in Table 1.

The biggest difference between the bipolar type and the monopolar type is the ‘configuration.’ While the monopolar type uses only one electrode placed on the skin and requires a grounding electrode on the other side, the bipolar type RF requires two electrodes to contact the skin and the current to flow from one electrode to another. The electric current, for this reason, could go as deep as half the distance between the two electrodes. The major limitation of this configuration is the depth of penetration. The monopolar device achieves high penetration of the emitted current, which serves as its main advantage and also its major drawback, which is associated with pain. The bipolar configuration is not as penetrating but provides more-controlled distribution of energy and less pain. In order to maximize the benefits of the bipolar RF, the electro-optical synergy (ELOS) technology where the light and laser are used together could be applied, or the FACES technology (functional aspiration controlled electrothermal stimulation) could be used, where vacuum is used to maximize the depth of penetration.4,19,20

The basic mechanism of treatment is similar to that of the monopolar type, where the emitted energy causes the contraction of the collagen in dermis, the inflammatory process, and the contraction of the fibrous septa.

Table 1 shows a summary of various studies using the bipolar RF technology.

In the ELOS system, which was developed by Syneron (Syneron Medical Ltd., Yokneam, Israel), the IPL, diode laser, or other light energy could be used to pre-heat the target tissue through photothermolysis and to lower the impendence of the tissue and, as a result, making it easier for the RF energy to penetrate the tissues. In addition, the optical components can be used for a direct reaction with fibroblasts, blood vessels, and the pigments in the epidermis. Some of the most well-known examples of ELOS technology include Aurora SR, which uses both of RF and IPL technology, Polaris WR, which combines RF with 900 nm diode laser, VelaSmooth which combines RF and infrared light of 700–2,000 nm with a suction system.12–27 Furthermore, each of the combined hand pieces could be selected and operated on a basic platform of single RF device according to the physician’s choice. With using three handpieces in a serial order (RF + IPL, RF + infrared light, RF + diode laser), we previously achieved the improvement of superficial dyschromia, erythema and wrinkles in a single treatment. The measurements proved that the melanin index (MI) and erythema index (EI) decreased, and the cutometer measurements also showed an improvement of the elasticity of the skin.28

The devices using FACES technology (Aluma System Lumenis, Inc., Santa Clara, CA) is composed of an RF generator, handpiece, and tips with two horizontal electrodes. This device creates a vacuum by means of suction. In a study with 46 patients who received treatments over 5 sessions in 1 to 2 weeks’ intervals showed statistically significant improvements in terms of the facial wrinkles and the skin elasticity. They also showed 50% improvements in the treatment of striae distensae.20,29

The most representative of the studies using bipolar RF are summarized in Table 1.

The fractional RF technology is a newly developed form of RF treatment, which is divided in two different types in the mode of energy delivery. One of them is an RF system using a microneedle, while the other is a system which is represented by the Matrix RF, using the bipolar RF to trigger a partial epidermal ablation. In as study using Renesis (Prmavea Medical, Inc. Fermont, CA), the generation of the controlled RF thermal zone (RFTZs) was confirmed. The advantage of this system is that, it can deliver the fractional RF energy using a microneedle with protection of the adnexal structures.30

In a study that evaluated the histological changes after fractional RF treatment, it was shown that molecular changes up to 10 weeks after the treatment, consecutive inflammatory reactions were observed starting from day 2 after treatment, which triggered the wound healing process and RFTZs were replaced by new collage as a result of the heat shock protein generation. Then, neoelastogenesis occurred to result in dermal remodeling.31

Based on several studies, it could be concluded that the fractional microneedle RF technology was effective in treating wrinkles and the scars of acnes.32–35

Matrix RF system (Syneron Medical, Ltd) is an RF treatment equipment that aligns the multielectrode pins in a pair to induce partial epidermal ablation. The nonhomogenous thermal wounds on the skin are directly delivered to the reticular dermis, while other areas than the target area are maintained intact, resulting in faster recovery from the wounds. The histological finding confirmed that the demarcated zones, which were identified by ablation, coagulation, necrosis, and subnecrosis, were generated to 450 um in depth. Along with that, higher energy and a low coverage rate resulted in good clinical outcomes while causing less pain to the patients.36

In a study with Asian population, the technology showed good clinical results on wrinkles, skin texture, or pores without post-inflammatory hyperpigmentation. In addition, the technology was also effective against acnes or acne scars.37–40 In the study by the author, clinical improvements were observed after 4 sessions in terms of the depressed scars and enlarged pores. In that study, all of MI, EI, and cutometer measurements showed significant improvements after treatment. In addition, histological observations showed that procollagen I, III, and elastin increased after treatment, causing less hindrance in daily lives due to shorter downtime caused by erythema or crust and less pain (unpublished data).

The development in RF technology for skin rejuvenation allowed a large variety of non-surgical anti-aging treatment. Up until now, RF treatments have been used for skin laxity, rhytides, acne vulgaris, scar, and cellulites. Most of the results of the treatments were positive, but the groups with the best chance of the positive results were the patients who showed the early signs of aging with mild to moderate degrees. In the meantime, the patients with profound skin fold or laxity required more invasive treatments or combined treatments. For this reason, treatments of these days usually combine other treatments, such as laser, botulinum toxin, or fillers, etc., to achieve the maximum effects with the minimum downtime. The RF will remain as the promising alternative treatment for ablative and nonablative laser and light based treatments. Further studies would be necessary to identify the ideal treatment parameters (energy level and the number of passes) and the treatment intervals, in a comparative study between different types of RF technologies and on new indications, as well.