How XERF radiofrequency works — monopolar delivery, two frequencies, heat and collagen, cooling
“How does radiofrequency make the skin tighter?” Knowing the mechanism makes it clearer what you can expect from XERF. This article explains how XERF creates heat, where the two frequencies, 6.78 MHz and 2 MHz, each heat, and why cooling comes with it. We should say first, though, that the data on heating by frequency come from computer simulation and porcine tissue, not from people.
The short answer
The principle of XERF is that monopolar radiofrequency current meets the electrical resistance of tissue and becomes heat, and that heat contracts collagen and stimulates renewal. XERF uses two frequencies, 6.78 MHz and 2 MHz; in a simulation and porcine tissue study, 2 MHz heated the fat layer broadly and deeply, and 6.78 MHz heated locally along the fibrous septa (Ko 2025; many of the authors are manufacturer employees; not a human study). The surface is protected by cooling, and the manufacturer’s published material is the sole source for XERF’s ICD gas cooling. Miso Clinic (4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, South Korea; +82-53-428-2700) builds on this principle by changing effectors by area to design where the heat lands (clinical judgement).
How does radiofrequency create heat?
When radiofrequency current passes through tissue, the tissue resists the flow. That resistance turns into heat — much as an electric blanket warms up. Unlike a laser, which relies on light being absorbed, radiofrequency tends to heat the whole volume the current flows through, regardless of skin colour.
| Type | How heat is produced | Miso Clinic |
|---|---|---|
| Radiofrequency (XERF · Density) | Electrical resistance of tissue | Available |
| Focused ultrasound (HIFU) | Ultrasound concentrated at one depth, coagulating point by point | Not available |
| Laser | Light absorbed by specific pigment · water | Not used for lifting |
Miso Clinic does not have focused ultrasound devices such as Ulthera. The difference between radiofrequency and ultrasound is also set out in HIFU and RF are not competing.
What is monopolar, and how does it differ from bipolar?
RF devices are divided by how the electrodes are placed. In monopolar delivery the effector on the skin is one electrode and a pad attached to the body is the other. As the current spreads from the effector towards the body, heat forms relatively deeply and widely. In bipolar delivery both electrodes are in one tip, so the current mainly passes through the shallow layer between them.
| Type | Electrode placement | Heat distribution | Example |
|---|---|---|---|
| Monopolar | One effector + a pad attached to the body | Deeper and wider | XERF |
| Bipolar | Two electrodes in one tip | Shallow layer between the two electrodes | The second stage of Density |
| Sequential | Monopolar → bipolar | Deep layer, then shallow layer | Density (Jeisys Medical) |
XERF uses monopolar delivery alone. Density delivers monopolar and then bipolar in sequence, so its structure is different. The difference between the two devices is in XERF vs Density: what is the difference?.
Where do 6.78 MHz and 2 MHz each heat?
What sets XERF apart is that one device uses two frequencies (the manufacturer calls it “dual monopolar”). There is one study that looked at how heat from the two frequencies is distributed (Ko 2025).
| Frequency | Where the heat formed | Caution in reading |
|---|---|---|
| 2 MHz | Broadly and deeply in the fat layer | Not measured in human skin |
| 6.78 MHz | Locally along the fibrous septa | Many of the authors are manufacturer employees |
The fibrous septa are bundles of connective tissue that run across the fat and link the skin to the deeper layers. This study is the rationale for the design, in that the two frequencies heat different places. However, no comparative study has been identified showing that using two frequencies in people is better than one.
What does the heat do inside the skin?
RF lifting aims at two stages. One is immediate contraction, in which heated collagen fibres shrink at once; the other is renewal over weeks to months after the heat stimulus.
- Right after treatmentA tight feelingThe heated tissue feels as if it has contracted. It is mixed with swelling and soon settles.
- About 4 weeksToo early to judgeIn a study of 20 Korean women, clinician assessment was not significant at 4 weeks.
- About 12 weeksFirst point of assessmentIn the same study there was significant improvement at 12 and 24 weeks.
- 4–6 monthsPeak in older-device dataIn data from older monopolar devices the peak was at 4–6 months. XERF data go up to 3 months.
So we do not judge the result by how it feels straight afterwards. Miso Clinic looks again at around 3 months, when the result has settled (clinical judgement). None of these timeline data has a control group.
Why is cooling needed?
While the heat of radiofrequency works in the deeper layers, the epidermis has to be protected. So RF devices usually use cooling as well. The manufacturer’s published material says XERF uses ICD gas cooling. For how well this cooling performs, the manufacturer’s published material is the sole source, and we could not find independently verified data.
Even with cooling, heat is heat. In data from an older monopolar device (2003, high-energy single-pass technique), blistering was 2.3% immediately and 3.8% within 72 hours. These are values from a time when the technique was different, not a current incidence (Fitzpatrick 2003). Fat atrophy was reported at about 4 per 10,000 treatments, with the observation that heavy anaesthesia blocks pain feedback (Narins 2006). One XERF study reported pain without anaesthesia of VAS 4–5 (Hwang 2025). Pain and anaesthesia are discussed in XERF side effects, read as a timeline.
What changes in treatment design once you know the principle?
The principle is the starting point for deciding “where, and how much”. Miso Clinic thinks about it as follows (clinical judgement).
- Layer thickness differs from person to person — in measurements of 30 cadavers, skin was 2.1 ± 0.4 mm and superficial fat 5.2 ± 1.9 mm (Lee 2021). We do not assume the same setting reaches the same depth.
- If the area differs, we change the effector — E40 and E60 for broad areas, i10 for narrow areas, i05 around the eyes.
- We read shot counts together with the tip set-up — “how many shots” alone does not allow comparison between clinics.
- We do not try to solve volume problems with heat — for hollowing we consider fillers first.
How to choose an effector is in XERF handpieces (effectors): how to choose, and the map of all our XERF columns is XERF lifting in Daegu: which skin it suits.
How XERF radiofrequency works: frequently asked questions
How does XERF tighten the skin?
Monopolar radiofrequency current meets the electrical resistance of tissue and becomes heat, and that heat contracts collagen and stimulates renewal.
What is the difference between XERF’s 6.78 MHz and 2 MHz?
In a simulation and porcine tissue study, 2 MHz heated the fat layer broadly and deeply, and 6.78 MHz heated locally along the fibrous septa (Ko 2025). It is not a human study, and many of the authors are manufacturer employees.
Is using two frequencies more effective than one?
No study comparing this in people has been identified. That the two frequencies heat different places is a rationale for the design, not evidence of a difference in effect.
Does XERF use bipolar as well?
No. XERF uses monopolar delivery alone. The device that delivers monopolar and then bipolar in sequence is Density.
Is the tight feeling right after treatment the result?
The tightness right after treatment is mixed with swelling and soon settles. In an RF study, clinician assessment was not significant at 4 weeks and significant at 12 weeks, so Miso Clinic looks again at around 3 months (clinical judgement).
Where can I have a XERF consultation in Daegu?
Miso Clinic is at 4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, in front of Exit 1 of Kyungpook National University Hospital Station. +82-53-428-2700. Weekdays 11:00–19:00, Saturdays 10:00–16:00 (no lunch break); closed Sundays and public holidays.
Read next
Product pages
Related: XERF product page
Who wrote this
Written and reviewed by Lee Chi-Hak, MD, director of Miso Clinic, Daegu. The treatment standards and injection design set out here are the ones we use in practice.
| Medical director | Lee Chi-Hak, MD |
|---|---|
| Address | 4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, South Korea · Exit 1, Kyungpook National University Hospital Station |
| Phone | +82-53-428-2700 |
| Hours | Weekdays 11:00–19:00 (lunch 13:00–14:00) / Saturday 10:00–16:00 (no lunch break) / Closed Sundays and public holidays |
| Columns | All clinical columns |
| Reference library | All booster and device references |
References
- XERF specifications — Lutronic published data: monopolar, 6.78 MHz + 2 MHz, handpieces i05 (5×10 mm · 400 shots) · i10 (10×10 mm · 300 shots) · E40 (20×20 mm · 600 shots) · E60 (20×30 mm · 600 shots). Classified in Korea as a general-purpose electrosurgical unit; advertising marking “General-purpose electrosurgical unit combination-2024-16-054”.
- XERF heating by frequency — Ko K et al., Lasers Med Sci 2025, PMID 41315066. Finite-element simulation and porcine tissue. 2 MHz heated the fat layer broadly and deeply; 6.78 MHz heated locally along the fibrous septa. Many of the authors are employees of the manufacturer, and this is not a human study.
- XERF cooling method — the description of ICD gas cooling in Lutronic’s published material. The manufacturer’s published material is the sole source, and we could not find independently verified data.
- The timeline of RF results — Cosmetics 2024;11(3):71 (20 Korean women: clinician assessment not significant at 4 weeks · significant at 12 and 24 weeks, device-measured firmness from week 4) · Weiss 2026 (84.6% at 30 days → 92.3% at 90 days) · Fitzpatrick 2003 and Edwards AF et al., Dermatol Surg 2013;39:104–110 (peak at 4–6 months). None has a control group.
- Timing and frequency of RF adverse reactions (older device) — Fitzpatrick R et al., Lasers Surg Med 2003;33:232–242 (86 subjects): blistering 2.3% immediately · 3.8% within 72 hours; second-degree burns in 21 of 5,858 treatments (0.36%) — figures for the 2002 high-energy single-pass technique, not a current incidence.
- Fat atrophy — Narins RS et al., Dermatol Surg 2006;32:115–124. Appears at 1–4 months (mean 2 months), about 4 per 10,000 treatments. Notes that heavy anaesthesia blocks pain feedback.
- Three XERF human studies — Hwang JK, Medical Lasers 2025;14(1):23–30 (20 subjects · one session · 12 weeks) · Weiss RA et al., Cureus 2026;18(3):e104546, PMID 41930066 (39 subjects · two sessions · 90 days, manufacturer support) · Erlich G et al., Lasers Med Sci 2026;41(1), PMID 42611100 (retrospective, 16 subjects · one session · 3 months). None of the three has a control group.
- Individual variation in facial layer thickness — Lee KW et al., Clinical Anatomy 2021;34(7):1050–1058, PMID 33583088. 3D measurement of 30 embalmed cadavers: skin 2.1 ± 0.4 mm, superficial fat 5.2 ± 1.9 mm.
- Density specifications — Jeisys Medical published data: sequential monopolar → bipolar delivery, up to 400 W, RIC automatic impedance adjustment, five-level gas cooling, real-time skin temperature display, tips ALPHA 600 · Eye 600 · Face 1,000 · Body 600 shots (the count sealed into each tip). Approved as a medical device by the MFDS; we could not verify the approval number itself.
- Medical advertising law — Medical Service Act of Korea, Article 56(2), which prohibits testimonial advertising, comparison with other clinics, superlative claims and advertising that guarantees or implies a guaranteed treatment effect.
- Miso Clinic practice guidance — indication criteria, site-by-site design, and the explanation and consent procedure. This is the source for every sentence marked as clinical judgement.
Everything in this column is general information and does not replace medical diagnosis or treatment. Effects and side effects vary with individual skin condition, age and underlying illness, and the same result is not guaranteed for everyone. Any decision to proceed should be made in an in-person consultation with a physician.
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