Why we look at skin thickness and facial fat when choosing a lifting treatment

In a study measuring 53 cadavers, facial skin ranged from 1.51 mm at the nose to 1.97 mm below the eye — about 1.3-fold. That is modest. The layer beneath is the problem: superficial fat ranged from 1.61 mm beside the nose to 5.14 mm around the mouth, roughly 3.2-fold.

Another dataset agrees. Across 30 cadavers scanned in three dimensions, facial skin averaged 2.1 mm and superficial fat 5.2 mm, with a standard deviation around 36% of the mean — that is, fat thickness varies widely between people.

Here is the practical consequence. Microfocused ultrasound cartridges are typically separated by 1.5 mm. The anatomical variation between people is larger than the device increment.

Microfocused ultrasound concentrates energy at a stated depth. Yet in a comparison of five devices using phantoms and cadaver tissue, the 3 mm cartridge produced coagulation in the dermis in front of the focus, and devices labelled with the same depth did not coagulate at the same place.

One thing should be stated plainly. We could not find a study measuring directly in humans that an individual fat layer pushes the focus off its target plane. That is an inference drawn from the two facts above, and it should be read as one.

Radiofrequency meets the same problem by another route. Near 1 MHz, the electrical conductivity of dermis is about eight times that of fat (roughly 0.25 against 0.03). Heating scales with conductivity and with the square of the field, so the same delivered energy warms differently depending on which tissue is there and how much.

In a study combining porcine tissue with computational modelling, a thinner fat layer produced higher temperatures. That is why the same setting does not transfer easily between a lean face and a fuller one.

Human data that actually varies the setting is scarce. In 31 subjects randomised split-face to compare monopolar radiofrequency tip sizes, the smaller tip was clearly better around the eyes. The nasolabial and marionette areas leaned toward the larger tip but did not reach statistical significance.

The point of that study is that the answer differs by region. It is enough to argue that one setting across the whole face is unlikely to be the best available plan.

Fairness requires this one. In 25 subjects followed for 12 months, neither skin thickness nor fat depth predicted response; only tissue mobility did (3.4 mm in responders versus 4.4 mm in non-responders).

We do not read that as a contradiction. The two things have different jobs.

• Thickness informs the design — at what depth, at what intensity.
• Laxity and mobility inform expectation — how much improvement is plausible.

The evidence for personalisation itself is still thin. A 16-week study in 20 subjects over 60 supported the direction, but the differences were 0.19 to 0.20 mm — below a millimetre — with no correction for multiple comparisons, and no stated rule for converting the ultrasound measurement into a cartridge choice, which makes it unreproducible.

Honestly stated, the most defensible gain from measuring thickness is not “better results” but “fewer bad outcomes.”

A review of 45 papers put fat atrophy at under 1% — uncommon — but attributed it to inappropriate depth selection. In a separate series of 39 patients, complications ran to 23%, including one case of persistent fat atrophy and three transient nerve palsies. There is also a recommendation against repeating 4.5 mm treatment within six months.

For what it is worth, several studies have found that body mass index does not predict facial skin or fat thickness. Being slim does not mean thin facial fat.

At Miso Clinic we do not apply lifting uniformly as a general firming measure. We weigh skin thickness, the degree of laxity and the distribution of facial fat together when judging suitability. In practice:

• We divide the face. The periorbital area, the cheek and the jawline do not get the same setting; the human data divided by region too.
• Less where it is hollow. Tightening hard over lost volume can read as gaunt.
• Mobility assessed separately. Expectation comes from there, not from thickness.
• Recent treatment history checked. Deep-plane passes are spaced out.
• No numbers promised. There is no basis for stating how many millimetres will lift.

Which treatment suits you depends on your skin condition, how much change you want, and what you have already had. The whole argument here is that the same device should be planned differently for different people.

• Lifting should vary with skin thickness and fat volume — the same subject in more depth
• Microfocused ultrasound versus radiofrequency · RF devices compared
• Facial sagging: which layer · Lifting checklist
• Density and XERF in Daegu · XERF reference · Density reference

Lee Chi-Hak, Director, Miso Clinic Daegu

4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, Korea (Exit 1, Kyungpook National University Hospital Station)

+82-53-428-2700 · www.clinicmiso.co.kr

• Any study measuring directly in humans that an individual fat layer moves the focus off its target plane — what we wrote is an inference.
• A reproducible rule for converting an ultrasound measurement into a setting.
• A large randomised trial showing thickness-matched personalisation beats a fixed setting.
• Any document giving a numerical safe upper limit by facial region.
• Any public metric comparing case volume or skill between clinics in Daegu — none exists.