What is the difference between HIFU 1.5mm and 4.5mm? How the effect changes with depth and how to choose between high frequency

The "type" of HIFU first determines the depth at which the ultrasonic heat is focused. Equipment commonly used in research has depths of 1.5mm, 3.0mm, and 4.5mm—the shallower depths reach the skin, while deeper depths reach the fascia beneath the skin (the membrane that supports the face)[1]. Which depths are combined depends on the location of sagging (skin laxity) and tissue thickness[1].

What changes with different depths?

Each depth targets a different layer where heat is delivered. 1.5mm targets the skin (dermis), 3.0mm targets the deeper skin, and 4.5mm targets the fascia beneath the skin or neck muscle layers[1].

Broadly speaking, shallow treatment aims for skin firmness and fine lines, while deep treatment aims for tightening from the foundation of the face. Which layer is reached also depends on the treatment location and tissue thickness[1]. Therefore, if the equipment has an imaging function, it becomes easier to select the depth while confirming the target layer[1].

Which depths are actually used with UTIMS A3 varies depending on the treatment facility. Here we explain based on research on HIFU overall.

Does combining depths increase the effect?

Some reports indicate that treatment at two depths produces better results than treatment at a single depth[2]. As the volume and layers of treatment increase, tissue movement and skin firmness scores increased, while pain intensity also increased[2].

In other words, "deeper and more" is not always correct. You decide the balance between the magnitude of change and pain to match your preferences.

In a study of 102 people who received shallow 2.0mm treatment every two weeks for 3 sessions on the eye area, mouth area, and neck lines, wrinkle improvement was observed at 10 weeks and 16 weeks, with no residual side effects[3]. If fine lines are a concern, shallow treatment may be emphasized.

How much change occurs? What about pain?

The change is roughly a "slight tightening." In a trial of 20 people treated with 4.5mm and 3.0mm on the lower face and under the chin, at 3 months, 7 out of 10 people showed clearly noticeable tightening[4].

Pain in the same trial averaged 3.00 on a 10-point scale[4]. Another study found average pain during treatment of 1.79 and after treatment of 0.64, with most resolving within about 2 days[5].

However, the number of studies is still limited. An analysis compiling research on 475 people noted that debate remains about HIFU's effectiveness[6].

HIFU versus high frequency (RF) — which should you choose?

According to guidelines from Japan's Association of Plastic Surgeons, both HIFU and high frequency are effective for sagging (skin laxity) and wrinkles, but their effects fall short of surgery or injections[7]. Scarring is rare with both methods[7].

HIFU's characteristic is that it focuses ultrasound at a single point to target deep layers such as the fascia beneath the skin[1]. High frequency is a different treatment with a different heat delivery method, so which suits you depends on the location and nature of your sagging (skin laxity).

Ultrasonic tightening may take several months to show final results[8]. If you want to time it with an important event, plan ahead or compare other methods.

What should I have examined during the consultation?

You should have examined the location and degree of sagging (skin laxity), the thickness of the skin and tissues beneath it, and whether your concern is "sagging (skin laxity)" or "fine lines." This determines which depths are used and how much treatment is given.

On top of that, confirm which depths will be used with UTIMS A3, pain management measures, and treatment intervals. Since you cannot decide between HIFU and high frequency based on an article alone, have your face examined in person to make an informed decision.