Radiofrequency vs. Ultrasound Lifting (The Evolution of EBD VI)
The full text of my column published in the November 2024 issue of D&PS.
RF devices fall broadly into three groups: bipolar RF, in which current passes between two electrodes; monopolar RF, in which current travels from the tip through a return pad elsewhere on the skin and back to the device; and unipolar RF, which generates an electromagnetic field rather than relying on conductive current flow. Inexpensive and home-use devices generally lack adequate output. Raising output while leaving out appropriate safeguards to keep costs down increases the risk of sparks from poor contact and other RF-related problems.
What temperatures stimulate collagen with RF?
A general equation for RF devices that stimulate dermal collagen is E=(I/A)²×Z×t. E is energy deposited in tissue; I is current flowing through area A; Z is tissue impedance, or resistance to alternating current; and t is the duration of current flow.
Impedance is one important determinant of temperature rise. It depends strongly on tissue composition and also changes with tissue temperature. The target range for immediate collagen conformational change and longer-term collagen production with nonablative devices such as monopolar RF is 45–65°C. During treatment, infrared surface measurements should remain at or above approximately 40–42°C. Relevant outcomes include collagen-remodeling contraction for tightening, fat-cell destruction, and nerve injury. Devices designed around 45°C recommend holding that temperature for 2 minutes 30 seconds for tightening and around 5 minutes for fat-cell destruction. Temperature–time combinations that could injure nerves must always be avoided. One study found that 1 minute at 50°C produced an effect equivalent to 10 minutes at 43°C (Dewhirst, 2003).
RF research initially focused on thermal destruction of cancers such as malignant hepatic tumors. Studies including “Essential Techniques for Successful Radio-frequency Thermal Ablation of Malignant Hepatic Tumors” helped establish how RF generates heat through molecular friction and how tissue responds at different temperatures.
One monopolar RF study found increased TGF-β1 and HSP72 immediately and at day 7, with a marked rise in HSP47 after day 30. TGF-β1 promotes collagen deposition, fibroblast and myofibroblast differentiation, and collagen secretion. HSP72 protects cells against thermal stress, whereas HSP47 plays a key role in collagen synthesis.
Expression of both type I and III collagen increased at days 7 and 30. Type I is the principal collagen in mammalian connective tissue and the final product of wound repair; type III predominates in the earlier granulation tissue. Increases in both indicate continuing improvement in skin volume, strength, and vitality. Yokoyama et al. reported similar findings in 2014: H&E staining showed increased dermal collagen at 1 and 3 months after RF.
Acute thermal shortening is followed by repair and regeneration over roughly 4 weeks. After 3 months, epidermal thickening and redevelopment of rete ridges become apparent. UV-related elastotic and dermal material decreases, while new collagen production rises substantially above the immediate post-treatment level. Neocollagenesis continues to 6 months, and damaged collagen decreases by 50%.
How does monopolar RF work?
These devices use monopolar capacitive RF energy. How is energy delivered to the deep dermis while protecting the surface? “Volumetric heating” means RF energy is delivered throughout a defined tissue volume at once. The amount reaching the dermis depends on tip size and shape and the tissue's inherent conductivity. The electrode sits inside the tip. When energized, the space between electrode and skin acts as an electrical capacitor, creating a stable electromagnetic field across the tip surface. At higher frequencies, RF behaves increasingly as a dielectric rather than a conductive interaction.
During a 6 MHz treatment cycle, the field reverses polarity six million times per second. This moves polar molecules and induces current within tissue. Current passes readily through hydrophilic structures such as the dermal collagen framework and underlying fibrous septa, but less readily through subcutaneous fat. Heating initially stimulates new collagen; excessive temperatures, however, convert its ordered crystalline structure into disorganized gelatin.
In 2002, Thermage, then called ThermaCool, became the first monopolar RF device cleared by the FDA for aesthetic use. Fitzpatrick et al. published a 2003 facial-rejuvenation study targeting periorbital tightening. Its method of comparing brow lift was widely cited in textbooks and became a standard in device-lifting research. Clinical papers including Javier Ruiz-Esparza's “The Medical Face Lift” (2003) and Michael Fritz's “Radiofrequency Treatment for Middle and Lower Face Laxity” (2004) extended its use across the face.
Brian D. Zelickson et al. demonstrated histological effects in “Histological and Ultrastructural Evaluation of the Effects of a Radiofrequency-Based Nonablative Dermal Remodeling Device” (2004), examining bovine tendon and human skin collagen. Edward B. Lack et al., in “Relationship of Energy Settings and Impedance in Different Anatomic Areas Using a Radiofrequency Device” (2005), reported variation between patients and facial areas. At low energy, mean impedance ranked zygoma, malar fat pad, then forehead; at high energy, forehead, zygoma, then malar fat pad. Eric Finzi et al. described the value of multiple-pass vectors in “Multipass Vector (mpave) Technique with Nonablative Radiofrequency to Treat Facial and Neck Laxity.” Nobuharu Kushikata et al. examined Asian skin in “Is Topical Anesthesia Useful in Noninvasive Skin Tightening Using Radiofrequency” (2005) and “Non-ablative Skin Tightening with Radiofrequency in Asian Skin.” Brian S. Biesman et al. introduced eyelid treatment in “Monopolar Radiofrequency Treatment of Human Eyelids: A Prospective, Multicenter, Efficacy Trial.”
Facial and neck rejuvenation may treat the whole region or separate cosmetic subunits. Upper-eyelid improvement is best approached by treating the forehead, upper lid, and temple together. Comprehensive periorbital treatment extends beyond the orbital rim across the eyelid and 1–2 cm below the cheekbone, sometimes including 1–2 cm lateral to the nasolabial and mesolabial folds. For effective neck treatment, the treated area is best extended to 2 cm above the jawline.
In “Monopolar Radiofrequency Facial Tightening: A Retrospective Analysis of Efficacy and Safety in Over 600 Treatments,” Robert A. Weiss et al. reported lower-face efficacy increasing from about 20% with an early single-pass approach to 80% with multiple passes. They described 17 adverse events among 600 cases. Erythema resolved within 5–20 minutes in 90%, while 5% had redness for 24–72 hours. Mild facial edema resolving within 24 hours was reported in 30%. Six patients had edema for up to a week and two for 1–2 weeks. Pain resolving within 48 hours was reported by 38%.
A 4 mm linear superficial crust healed completely within a week, and a slight cheek depression resolved spontaneously over 3.5 months. Three cases of acneiform subcutaneous erythematous papules and one erythematous patch appeared within 3 days and resolved within 10. Three patients had neck pain for 1–4 weeks. For treatment discomfort, the study used 4% lidocaine cream (LMX4, Ferndale Labs, Ferndale, MI) or 4% tetracaine plus 1% lidocaine cream (Lasercaine, Boswell West Pharmacy, Sun City, AZ), along with oral agents including valdecoxib 20–40 mg, diazepam 5–10 mg, or acetaminophen 500 mg with oxycodone 5 mg.
Monopolar RF and collagen renewal
One large case series is Jeffrey S. Dover et al.'s “Results of a Survey of 5,700 Patient Monopolar Radiofrequency Facial Skin Tightening Treatments: Assessment of a Low-energy Multiple-pass Technique Leading to a Clinical End Point Algorithm” (2007). It supported the clinical value of the newer low-energy, multiple-pass protocol in 5,700 cases. David Kist et al., in “Ultrastructural Evaluation of Multiple Pass Low Energy Versus Single Pass High Energy Radio-frequency Treatment” (2006), showed histologically that low-energy multiple passes produced more collagen than a high-energy single pass. Yokoyama et al., in “Histologic Study of Collagen and Stem Cells After Radiofrequency Treatment for Aging Skin” (2014), confirmed increases in type I and III collagen. Dong Hye Suh et al., in “Comparative Histometric Analysis of the Effects of High-intensity Focused Ultrasound and Radiofrequency on Skin” (2015), found significantly greater papillary-dermal collagen and elastin increases with monopolar RF than HIFU. Javier Ruiz-Esparza proposed key treatment areas in “Nonablative Radiofrequency for Facial and Neck Rejuvenation. A Faster, Safer, and Less Painful Procedure Based on Concentrating the Heat in Key Areas: the Thermalift Concept.” He reported a 78-year-old woman maintaining results for 14 months after one treatment and described neck improvement by treating the mandibular angle and posterolateral hairline.
Semchyshyn et al., in “Does Laser Inactivate Botulinum Toxin?”, found that monopolar RF after botulinum toxin did not affect efficacy. Studies of RF over fillers include “Effects of Monopolar Radiofrequency Treatment Over Soft-tissue Fillers in an Animal Model: Part 1” (2005) and “Effect of Monopolar Radiofrequency Treatment over Soft-tissue Fillers in an Animal Model: Part 2” (2006). Alam et al. studied RF and HA filler, reporting no reduction in filler effect after RF and suggesting that the combination could assist overall skin tightening.
The RF group formed more collagen than the untreated group, although the difference was not significant. RF did not adversely affect the filler's collagen response or duration and did not increase unwanted thermal injury after filler placement.
In “Clinical Parameters for Predicting Efficacy and Safety with Nonablative Monopolar Radiofrequency Treatments to the Forehead, Face, and Neck” (2007), Sasaki et al. examined nonresponse. Responders and nonresponders did not differ in age, skin thickness, or fat thickness, but did differ in mobility scores and wrinkle and fold depth.
Dong Hye Suh et al. surveyed aesthetic physicians in “Monopolar Radiofrequency Treatment in Asian Skin: A Questionnaire-based Study” (2011). Skin thickness and the degree of laxity and wrinkling were judged the two strongest determinants of responsiveness. Their 2020 “A Survey on Monopolar Radiofrequency Treatment: The Latest Update” found frequent neck and abdominal treatment and a strong tendency toward regular repeat sessions. Most patients had received more than five treatments, and nearly 20% had received 11 or more. The same group, in “Monopolar Radiofrequency Treatment in Asian Skin: Do Multiple RF Treatments Over Time Have Beneficial Effects? An Observational Report with Long-term Follow-up in Eight Patients” (2013), compared photographs from 2004–2010 in patients with and without regular RF. Those treated regularly over time maintained a more youthful appearance.
Figure 1. Bovine tendon. A, Control cross section shows normal collagen fibrils. B, Longitudinally sectioned control specimen shows normal collagen fibrils. C, Specimen after radiofrequency (RF) treatment (500 J with medium cooling) 0 to 1 mm below the surface. Large arrows point to a cross section of partially denatured collagen fibrils showing loss of electron density and sharp borders. Small arrows point to normal fibrils. D, Specimen after RF treatment (500 J with medium cooling) 0 to 1 mm below the surface. Large arrows point to longitudinal section fibrils at the junction between a normal-appearing area and a partially denatured area with loss of electron density and sharp borders (original magnification ×17 280). Bars indicate 300 nm. Source: “Histological and Ultrastructural Evaluation of the Effects of a Radiofrequency-Based Nonablative Dermal Remodeling Device,” Brian D. Zelickson et al., Arch Dermatol. 2004;140(2):204–209. doi:10.1001/archderm.140.2.204.
What other RF lifting technologies are available?
Bipolar RF mainly passes current between two electrodes. Energy initially tended to concentrate in the epidermis rather than the dermis, limiting efficacy and increasing surface-burn risk. Several approaches were developed in response. Penetration is generally around 50% of electrode spacing, while visible collagen denaturation occurs at only around 10–20%. Pre-cooling lowers epidermal conductivity to direct current deeper; targeted diode-light preheating lowers dermal resistance. Vacuum-assisted systems were also introduced, including devices that hold tissue under suction while delivering high-voltage pulses to increase fat-cell injury.
Figure 2. Collagen molecular structure. Source: https://scienceon.kisti.re.kr/commons/util/originalView.do?cn=TRKO202000002637&dbt=TRKO&rn=&page=3&keyword=undefined.
Needle RF emerged in Korea around 2009. Fractional RF is a form of bipolar RF with multiple mini-electrodes, mainly addressing firmness, texture, tone, wrinkles, and pores. Korean manufacturers developed needle RF by combining microneedling and RF. Combining needles with lasers was also considered, but it proved difficult to fit a laser fiber into a fine needle. Devices differ substantially in how the needles enter tissue. Early Korean-developed systems showed useful clinical results for laxity and double chins, with Scarlet, now Sylfirm X, among representative examples.
How did ultrasound lifting evolve?
Diagnostic ultrasound generally uses frequencies from 1 to 15 MHz. Higher frequency improves resolution but reduces penetration depth. Sound travels at a constant speed within a given medium or tissue. The piezoelectric effect occurs when compression and expansion of a crystal generate positive and negative charges on opposite sides. Conversely, applying alternating current makes the crystal repeatedly contract and expand, generating ultrasound through the reverse piezoelectric effect. Ultrasound transmits energy through alternating compression and rarefaction. Transverse waves oscillate perpendicular to travel, while longitudinal waves oscillate parallel to it. Transverse waves do not occur in liquids or air; ultrasound in the body is predominantly longitudinal.
HIFU was used from the 1990s for conditions including prostate and breast cancer, then investigated for fat-cell destruction. Lifting observed during this work led to facial devices. Ultherapy was originally developed to test fat reduction using HIFU that had been used to coagulate prostate tumors. Fat reduction was not clinically clear, but improved firmness in loose fascia and subcutaneous tissue led to its use for lifting. Whereas RF delivered energy through successive skin layers, HIFU introduced the concept of heating and contracting the SMAS while leaving the skin intact.
Ultherapy received FDA clearance for brow lifting in 2009, chin and neck lifting in 2012, and the décolletage in 2014. Korean patients' preference for a slim “V-line” jaw and smooth lower face, even at older ages, helped launch the global HIFU trend. While earlier rejuvenation devices mainly entered practice to reduce eye and nasolabial wrinkles, HIFU became popular through reports of a sharper jawline and a smaller-looking face.
Classys's Shurink advanced the trend further, achieving international success with a reputation for less pain and faster effects than other HIFU systems. The company attributes this combination to high peak power. Its MF2 cartridge is designed for the eye area. MF6 and MF9 can be used for tightening and fat reduction on the abdomen, thighs, upper arms, axillae, knees, calves, and ankles.
Years of use have produced substantial practical knowledge. HIFU uses tips with different powers and depths to create thermal points. Outcomes depend on their depth, energy, and number in each facial area, and treatment must also suit facial shape. Brow droop, eye wrinkles, cheek pores, jawline fat, and severe laxity call for different plans.
Ulthera began regularly updating practitioner guidelines soon after its 2008 approval. FDA clearances defined treatment areas, while comparative studies favored multiple depths and directions. Recommended line counts increased with successive guidelines. Increasing treatment density became a common first strategy for double chins. Facial fat atrophy, recorded as an adverse effect of HIFU, was deliberately used to reduce submental fat through denser treatment.
Another common approach removes subcutaneous fat anterior to the platysma, using liposuction or another method, before HIFU. In this context, Ulthera recommended 504 total lines for the face and neck in 2011; the American physician Sasaki proposed as many as 960.
Higher counts created two main problems: pain during longer sessions, and excessive fat loss that could make the face look older. In Korea in the 2010s, controversy surrounding propofol made some patients reluctant to choose sedation, adding to hesitation about Ultherapy. Concern about hollowing even led to an anti-Ultherapy online community sharing photographs of gaunt faces. To reduce these problems, many clinicians now use lower intensity with more lines and favor 3.0 mm over 4.5 mm treatment, since the deeper setting can affect the fat layer.
Detailed manufacturer guidance also contributed to HIFU's success. Ulthera repeatedly updated its treatment maps. I suspect these revisions drew in part on a 2007 study finding greater lifting when dot lines were oriented vertically.
Clinical research on HIFU
Adrian Lim et al.'s “High Speed Low-pain Micro Focused Ultrasound Tightening of the Lower Face and Neck” (2017) reflects clinicians' view that Shurink combines clear results with advantages in pain and treatment time. EJ Ko et al.'s “Efficacy and Safety of Non-invasive Body Tightening with High-intensity Focused Ultrasound (HIFU)” (2017) showed how its speed also helps with time-consuming body treatment. Hyuck Hoon Kwon et al., in “Tightening and Reduction of Unwanted Submental Fat Using Triple-layer High-intensity Focused Ultrasound: Clinical and 3-dimensional Imaging Analysis,” visually demonstrated submental fat reduction. Man-Lok Lio et al.'s “Quantified Facial Rejuvenation Utilizing High Intense Focus Ultrasound with Multiple Penetrative Depths” (2022) proposed objective measures for lifting outcomes.
Won Jong Oh et al., in “Effect of High-intensity Focused Ultrasound on Eyebrow Lifting in Asians” (2019), demonstrated lifting with a 3 mm transducer. Gyu Sik Jung et al., in “High-Intensity Focused Ultrasound: A Satisfactory, Non-invasive Procedure for Crow's Feet Wrinkles” (2019), found a 2 mm transducer effective for eye wrinkles. Hye Chan Jeon et al.'s “A New Treatment Protocol of Microfocused Ultrasound for Lower Eyelid Fat Bulging” (2021) reported benefit for lower-eyelid fat bulging at 2 mm. Hye Sung Han et al.'s “Safety and Efficacy of High-intensity Focused Ultrasound for Treatment of Periorbital, Perioral, and Neck Wrinkles: Prospective Open Single-center Single-arm Confirmatory Clinical Trial” (2022) likewise supported 2 mm treatment for these areas. Papers using Shurink's 1.5 mm tip have also reported effects on pigmentation, including melasma.
(To be continued in the next issue)
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