What do Ulthera's 4.5, 3.0 and 1.5 mm depths each do?

By Dr. Young Jun Kim, Medical Director, Violacell Plastic Surgery · Board-certified plastic surgeon (Korea)

Each depth is a separate transducer that focuses ultrasound heat at one fixed distance below the skin surface. The 4.5 mm transducer aims at the deeper supporting layer (SMAS) and, in the neck, the platysma muscle, for lift; the 3.0 mm transducer aims at the deep part of the skin for firmness; and the 1.5 mm transducer aims at the upper skin for texture and fine lines. Most plans combine the three, because tissue thickness changes from one area of the face to the next.

Knowing what each depth is for helps you understand a treatment plan, and why the mix of depths matters more than any single number.

How a fixed depth works

Ulthera is microfocused ultrasound with visualization (MFU-V). The transducer, the cartridge attached to the handpiece, focuses ultrasound energy onto small points at a set depth, much as a lens focuses light. At each point the tissue is heated briefly above about 60 °C, enough to make collagen contract, while the skin surface above is left largely unaffected. One pass lays down a short row of these points, which clinics count as one line or shot.

The depth is built into the transducer. Pressing harder does not send the energy deeper; treating another layer means switching to another transducer. Each one also uses a different ultrasound frequency: lower frequencies focus deeper.

Depth	Frequency	Layer it usually reaches	Main purpose
4.5 mm	4 MHz	The SMAS, and the platysma muscle in the neck, where tissue is thick enough	Lift of the deeper supporting layer along the jawline, lower face and under the chin
3.0 mm	7 MHz	The deep dermis and the top of the fat beneath it	Firmness of the skin itself; also used where tissue is too thin for 4.5 mm
1.5 mm	10 MHz	The superficial dermis	Texture, pores and fine lines in selected areas

Narrower versions of the 4.5 mm and 3.0 mm transducers exist for small or curved areas, such as under the chin or beside the nose. They reach the same depths with a shorter row of points.

4.5 mm: the supporting layer

The SMAS (superficial musculoaponeurotic system) is a thin, firm sheet that surrounds the facial muscles and holds the fat and skin above it in place. It is the layer a surgical facelift lifts. Heating it at 4.5 mm aims to tighten this sheet so that the contour above it sits slightly higher and firmer. Dr. Kim writes that concentrating energy in the SMAS is what gives the most lifting effect.

The deep depth is used where the soft tissue is thick enough to hold it: usually the lower cheek, jawline, under the chin and the neck. It is usually avoided or reduced where bone is close to the surface, such as the temple and forehead in many people, because energy on bone is painful and adds little. Near the edge of the lower jaw, where the nerve branch to the lower lip runs, it is placed with care.

3.0 mm: the deep skin

The dermis is the thick inner part of the skin, where most of its collagen sits. At 3.0 mm the focus lands in the deep dermis and, in many areas, the top of the fat just below it. This depth aims at firmer skin rather than at the deeper sheet. It is also the main depth in areas where the tissue is too thin for 4.5 mm, such as parts of the temple and forehead.

1.5 mm: the upper skin

The 1.5 mm transducer works close to the surface, in the superficial dermis. Dr. Kim describes it as the depth for pores and skin texture. Because the energy is near the surface, it is placed carefully: too much at this depth can leave temporary raised lines or, rarely, surface marks. Around the eyes, treatment stays outside the bony rim of the eye socket.

Energy in the fat layer

Between the skin and the SMAS lies the subcutaneous fat. Dr. Kim writes that energy delivered into the fat layer has a volume-control effect. That can help a soft, full lower face look neater, but it is also why deep energy is placed conservatively in a face that is already lean. This is discussed in Can Ulthera make the face look hollow?

Why the same depth lands in different layers

A transducer's depth is fixed; a person's anatomy is not. The same 4.5 mm focus may sit in the SMAS over the jawline of one person, in the fat over the jawline of another, and close to bone at the temple of a thin person. This is why the on-screen image matters. Before each pass, the transducer shows a cross-section of skin, fat, the SMAS or muscle, and the bright line of bone where bone is near. It lets the practitioner check whether the intended layer is actually present at that depth in that spot.

Ultherapy PRIME extends this image to about 8 mm, compared with about 4.5 mm, which helps where the deeper layers are hard to see. See Ulthera or Ultherapy PRIME: what actually changes?

Combining depths for each face

An older rule of thumb was to use mostly the 4.5 mm depth when a face had more fat. Dr. Kim describes moving away from that, towards combining 4.5, 3.0 and 1.5 mm according to skin thickness and structure. As illustrations he cites proportions such as 6:3:1 in many women and 5:3:2 in many men. These are examples of how a mix can look, not a fixed formula; the actual proportion is set for each face after examination.

The mix is shaped by questions like these:

Where is the sagging mainly happening: the jawline, under the chin, the brow?
How thick are the skin and fat in each area?
Is the main concern lift, firmness of the skin, or texture?
Where is bone close to the surface?
Where do nerves run near the surface?
Is the face already lean in some areas?

Common misunderstandings

"4.5 mm is the strongest, so more of it is better." It reaches the deepest layer, but where tissue is thin it can land near bone, hurt more and add little. In a lean face it can also take away volume that should be kept.
"Using all three depths means more lift." Each depth does a different job. Lift comes mainly from the deeper layer; the shallower depths work on the skin.
"1.5 mm barely matters." For texture and fine lines it is the relevant depth, and in thin areas it may be the main one used.

Risks by depth

All depths can cause discomfort, redness, swelling, tenderness and bruising. The deeper depth is usually the most uncomfortable, especially over bone, and is the one most associated with rare temporary nerve weakness when placed near nerve paths. The shallow depth is more associated with temporary raised lines and, rarely, surface burns if contact is poor or energy too high. Correct depth choice, even contact and avoiding bone and higher-risk zones are the main ways to reduce these.

When no depth is enough

All three depths tighten tissue that is still roughly in place. None removes excess skin or lifts clearly hanging jowls or neck skin, where a mini facelift or facelift is usually more effective. Lost volume calls for something like Sculptra. For fine lines and skin elasticity, Dr. Kim notes in his answers to patients that radiofrequency such as Thermage is better suited than focused ultrasound. As a plastic surgeon trained in facial surgery, he will say when surgery is the better answer, although he does not perform surgery at Violacell.

Why it matters who plans it

The depths are tools; the plan decides which goes where. Dr. Kim learned the layers of the face, the SMAS, the fat compartments and the nerve paths, in plastic surgery training at Chonnam National University, where he was later a clinical professor. He designs Ulthera from the live ultrasound image and palpation, combines the three depths for each face instead of defaulting to one, and was invited to the Ultherapy PRIME Asia launch in Seoul in 2025. Why Dr. Kim for Ulthera

Common questions

Which Ulthera depth gives the most lift?

The 4.5 mm depth, because it reaches the SMAS, the supporting layer that a facelift also lifts. It is only useful where tissue is thick enough; in thin areas it can land near bone.

Why not use 4.5 mm everywhere?

Tissue thickness varies. Over thin areas such as the temple and forehead, 4.5 mm can reach bone, which is painful and adds little, and in lean areas deep energy may reduce volume that should be kept. Shallower depths suit those areas better.

What do ratios like 6:3:1 mean?

They describe how lines might be divided between the 4.5, 3.0 and 1.5 mm depths. Dr. Kim cites 6:3:1 in many women and 5:3:2 in many men as illustrations. The real mix is decided for each face after examination.

Does the 1.5 mm depth help with fine lines?

It works on the upper skin and is used for texture, pores and fine lines in selected areas. For fine lines and skin elasticity as the main goal, radiofrequency such as Thermage may suit better.