The Meaning of HIFU Numbers — 1.5mm and 4.5mm Are Completely Different Treatments

DIORE CLINIC

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Hello, I’m the chief director of Diorre Clinic near Gangnam Station.

Let me start with the two questions I hear most often in consultations. "I’m looking into HIFU lifting—what exactly do the numbers 1.5mm, 3.0mm, and 4.5mm mean?" and "I heard Ulthera, Shurink, and CoolSonic are all HIFU, but do different handpieces change the results?"

The answer is the same: the basic principle of HIFU (High Intensity Focused Ultrasound) is identical across all devices, but which area is treated with which depth tip makes the actual results feel completely different. In this article, we’ll organize the expected effects by tip depth and explain which parts of the face the handpieces of major devices are suited for.

First, the principle: how a "thermal coagulation point" changes the skin

HIFU works in a way similar to concentrating sunlight at a single point with a magnifying glass, focusing ultrasound energy at a specific depth within the skin to create a 60~70°C thermal coagulation point (TCP, Thermal Coagulation Point). This micro thermal injury triggers a natural healing response, generating new collagen and elastin, causing tissue contraction and leading to lifting and tightening effects.

The key is at what depth this TCP is created. Because the skin layer being stimulated changes, the expected effect also changes, so HIFU devices come with different cartridges (tips) for each depth.

Tip depth determines the effect

1.5mm — Upper dermis (epidermal-dermal junction)

The shallowest tip, it stimulates the upper dermis close to the skin surface.

• Main effects: improved skin texture, reduction of fine lines, pore refinement, more even skin tone
• Suitable areas: delicate areas with thin skin such as around the eyes, forehead, and around the mouth
• Features: This is closer to skin renewing (skin regeneration and texture improvement) than lifting. It is especially useful for thin areas where deeper tips are difficult to use, such as the eyelids and around the lips.

Shurink Universe applies the dedicated Derma Shurink tip at this depth, forming thermal points only in the upper dermis without affecting the fat layer and improving elasticity.

2.0mm — Mid-dermis (Shurink Universe exclusive)

A newly added depth in Shurink Universe, handled by the Eye Shurink tip.

• Main effects: tightening around the eyes, improvement of under-eye wrinkles, reduction of drooping at the outer corners of the eyes
• Suitable areas: delicate areas such as around and under the eyes
• Features: Slightly deeper than 1.5mm, but optimized for the thin skin around the eyes.

3.0mm — Deep dermis

The core mid-depth tip, targeting the collagen-rich zone in the lower dermis.

• Main effects: skin tightening, increased collagen density, improved elasticity, pore improvement, reduced fine lines
• Suitable areas: medium-thickness skin such as the cheeks, jawline, forehead, and neck
• Features: A histological study published in the Journal of Cosmetic Dermatology in 2025 confirmed that after HIFU treatment at 3.0mm depth, collagen types I and III synthesis and elastic fibers increased significantly in the dermis. This is the key depth for building firm, dense elasticity.

4.5mm — SMAS layer (Superficial Musculoaponeurotic System)

The deepest tip, delivering ultrasound energy all the way to the SMAS layer, which is directly addressed in facelift surgery.

• Main effects: powerful lifting, improvement of sagging cheeks and jawline, creation of a V-line contour, reduction of double chin
• Suitable areas: thick-skin areas with visible sagging such as the cheeks, jawline, and neck
• Features: The SMAS layer is a fibrous connective tissue that links skin and muscle, so when this layer contracts, the entire skin surface is physically pulled upward. That is why the 4.5mm tip is called the core of lifting. However, because the energy is delivered deeper, it tends to be more painful than other depths and may feel more pronounced near the bone.

Note: If the 4.5mm tip is used indiscriminately in areas with thin fat or existing hollowness, it can lead to fat loss side effects such as sunken cheeks. This is why precise anatomical judgment by the practitioner is so important.

Comparison of effects by depth at a glance

How handpieces differ by device

Ultherapy

The world’s first ultrasound lifting device made by Merz in the U.S., and the gold standard for HIFU approved by the FDA.

• Handpieces (transducers): three types, 1.5mm / 3.0mm / 4.5mm
• Greatest strength: Patented DeepSEE™ real-time ultrasound imaging technology allows the practitioner to directly monitor the depth and structure of the skin layers during treatment while delivering energy. As a "see-while-you-treat" HIFU, it offers the highest precision and safety.
• Area-specific use: forehead and eyebrow lifting (1.5mm), cheek and jawline tightening (3.0mm), lower face and neck lifting (4.5mm)
• Effect duration: about 12~18 months, recommended once a year
• A device whose efficacy and safety have been validated by more than 110 clinical papers.

Shurink Universe

A second-generation HIFU device developed by Classys in Korea, approved by the Ministry of Food and Drug Safety.

• Handpieces: dual system of the existing handpiece (ULTRA F) + pen-type handpiece (ULTRA BOOSTER)
• Cartridges: 7 types in total (4 ULTRA F cartridges: 1.5mm / 2.0mm / 3.0mm / 4.5mm + 3 booster-only cartridges: 1.5mm / 3.0mm / 4.5mm)
• Greatest strength: The pen-type booster handpiece allows precise treatment of curved areas such as the glabella, around the eyes, philtrum, and chin tip. With the addition of MP mode (line-shaped) to the existing dot type, it creates about 400 thermal coagulation points per shot in a dense pattern.
• Area-specific use: covers the whole face from forehead, cheeks, jawline, to neck by combining depth-specific cartridges
• Effect duration: about 3~6 months, recommended 2~3 treatments per year

CoolSonic

A next-generation domestic HIFU device that promotes "HIFU without pain."

• Handpieces: dual system of Line type + Pen type
• Greatest strength: the patented ACC™ (Active Conduction Cooling) cooling system and TDT heat diffusion technology are key. The cooling module built into the handpiece cools the skin surface at the same time ultrasound energy is delivered, significantly reducing pain compared with conventional HIFU.
• Area-specific use: used across the cheeks, jawline, and neck by combining line and pen types
• Effect duration: about 6~12 months
• A good alternative for those who want the effects of Ultherapy but have hesitated because of pain.

Handpieces by device, side by side

Which depth combinations work for each facial area?

Forehead and eyebrows: 1.5mm (texture) + 3.0mm (tightening) → eyebrow lifting, reduction of forehead wrinkles

Around the eyes: 1.5mm or 2.0mm → improvement of fine wrinkles around the eyes, lifting of drooping outer eye corners (deep tips are not used around the eyes)

Cheeks and cheekbones: 3.0mm (dermal tightening) + 4.5mm (SMAS lifting) → improvement of sagging cheeks, reduction of nasolabial folds

Jawline and double chin: 4.5mm (SMAS lifting) + 3.0mm (dermal support) → V-line formation, reduction of double-chin volume, sharper jawline

Neck: 3.0mm + 4.5mm → improvement of neck wrinkles, tightening of loose neck skin

In actual treatment, it is rare to use only one depth for a single area; instead, tips of multiple depths are combined layer by layer to deliver energy from the dermis down to the SMAS in a multilayered way. This is HIFU’s "multilayer approach," and the reason the practitioner’s experience and judgment ultimately determine the result.

What foreign patients in Gangnam ask when choosing HIFU

Foreign patients usually begin with "Which HIFU device is the best?" and, as the consultation progresses, move on to more specific questions about combinations.

• "Do I need both HIFU and Thermage?" — Yes, there is a reason combination consultations are so common. HIFU lifts the SMAS layer, while Thermage (radiofrequency) stimulates collagen in the dermis to tighten. In building terms, HIFU handles the steel frame, and Thermage handles the exterior finish.
• "Is Sofwave also a type of HIFU?" — Sofwave uses ultrasound, but it is a separate device family with a different focusing method, so it is difficult to compare it one-to-one with the 1.5~4.5mm tip system covered in this article. In consultation, we compare it with HIFU options based on skin thickness and desired duration of results.
• "Can HIFU be combined with injectable treatments like Rejuran or Lituo?" — Yes. HIFU provides structural lifting, while collagen-regenerating injections like Rejuran and Lituo help supplement the skin’s texture and density, so the approaches are different. Many foreign patients combine the two in the same visit.

Frequently asked questions

Q1. Do I have to receive all of 1.5mm, 3.0mm, and 4.5mm?

No, all depths do not necessarily need to be used. The optimal combination depends on skin thickness, fat volume, degree of sagging, and desired effect. For example, for someone with thin skin and sunken cheeks, it is safer to minimize the use of 4.5mm and focus on 1.5mm and 3.0mm.

Q2. Is Ultherapy more effective than Shurink or CoolSonic?

All three devices use the same HIFU principle. Ultherapy has high precision with real-time image guidance (DeepSEE™) and has been validated by more than 110 clinical papers, so its effects and duration after a single treatment tend to be longer. Shurink and CoolSonic are less painful and more affordable, making them suitable for regular maintenance treatments.

Q3. Can HIFU make the cheeks look hollow?

The ultrasound energy from the 4.5mm tip may affect fat cells as it passes through the fat layer. If performed at high output in areas with little fat, sunken cheeks may occur, so it is important to use the 4.5mm tip only in areas with enough fat and avoid areas at risk of hollowness.

Q4. When do results appear after HIFU?

You may feel slight tightening from tissue contraction immediately after treatment, but the full effect appears at its maximum 2~3 months later, when collagen is regenerated. Improvement then continues gradually up to 6 months.

Q5. Can Thermage and HIFU be done together?

Yes, it is a very good combination. HIFU lifts the deep SMAS layer, and Thermage (radiofrequency) stimulates collagen in the dermis for tightening. In building terms, it is like HIFU supporting the steel structure and Thermage firmly finishing the exterior.

Q6. Is CoolSonic really not painful?

It is true that the pain is significantly reduced compared with conventional HIFU. The ACC™ cooling system cools the skin surface and blocks heat and pain. In most cases, treatment can be performed without anesthesia, with only a slight feeling of warmth or soreness.

Conclusion

With HIFU, the results can vary greatly even with the same device depending on the depth of the tip and the treatment area. Smoothing skin texture with 1.5mm, strengthening the dermis with 3.0mm, and lifting the SMAS layer with 4.5mm — this multilayered approach is the secret to a natural yet effective lift.

Most importantly, it is essential to choose the right depth and device for your skin condition and to receive treatment from experienced medical staff who understand anatomical structure accurately. If you’re curious about HIFU lifting, feel free to book a consultation. After directly evaluating your skin thickness and degree of sagging, we will suggest the optimal treatment plan.

References

1. Kim HJ, et al. Do Different High-Intensity-Focused Ultrasound Frequencies Have Different Effects? A Histological Analysis Correlated With Patients' Subjective Assessments. J Cosmet Dermatol. 2025;24(2):e14506.
2. MacGregor JL, Tanzi EL. Microfocused ultrasound for skin tightening. Semin Cutan Med Surg. 2013;32:18-25.
3. Ultherapy official clinical data: more than 110 clinical papers (60 peer-reviewed + 50 clinical studies).
4. Official product information for Classys Shurink Universe: 7-cartridge system, MFDS approval.
5. Fabi SG. Noninvasive skin tightening: Focus on new ultrasound techniques. Clin Cosmet Investig Dermatol. 2015;8:47-52.