XERF shallow and deep modes versus HIFU: what are the differences? How to choose a sagging (skin laxity) treatment

The difference between XERF (Zerf) shallow and deep modes lies in the radiofrequency frequency used and the depth targeted for heating[1][2]. The shallow mode uses 6.78 MHz to target skin layers, while the deep mode combines 6.78 MHz and 2 MHz in a single application to target deeper support layers[1]. However, no research has directly measured heat depth in the human face[3]. Including HIFU, no device is reported to produce changes as large as surgery or injections[4].

XERF shallow and deep modes: what is the difference?

The difference is the layer where you want to build heat. The shallow mode targets skin layers and fine support fibers beneath the skin.[1] The deep mode aims to reach deeper into the fascia (SMAS) and ligaments that connect facial tissue.[1].

In mathematical modeling and animal studies, the 2 MHz frequency transmitted heat more broadly and deeply, warming the fat layer.[2] At 6.78 MHz, heat tended to accumulate along fibers running through the fat.[2] When the two are combined, strong heat is generated around the boundary between skin and fat.[2].

In minipig studies, this setting produced no visible signs of fat cell damage.[2] However, these are computational and animal results. Human studies have not measured depth either, and the authors themselves note that explanations of deeper penetration include speculation.[3].

How does XERF differ from other radiofrequencies?

XERF is monopolar (single-electrode) type, applying one electrode and sending electrical current into the body.[1] Monopolar devices are reported to reach depths of up to about 20 mm, while bipolar devices warm a shallower range of 1–4 mm.[5].

Bipolar is often used for fine lines and mild sagging (skin laxity); microneedle RF, which delivers radiofrequency through needles, is frequently used for acne scars and skin texture.[6] Even though they are all "radiofrequency," each targets slightly different concerns.

How does HIFU differ from radiofrequency in how heat is delivered?

Radiofrequency heats broadly across an area, while HIFU concentrates ultrasound at a small point.[7] HIFU delivers heat to a depth of approximately 1.5–4.5 mm from the skin surface and can target the fascial layer.[8][7].

Radiofrequency requires cooling the skin surface while applying it; some HIFU devices allow you to monitor depth on a screen.[7] XERF has cooling and a skin-temperature monitoring mechanism to prevent burns and excessive fat loss.[1].

What level of results can be expected?

Results are modest and suited to mild sagging (skin laxity). The Japan Society of Aesthetic Plastic Surgery guidelines rate both radiofrequency and HIFU as "weakly recommended," and note that efficacy does not reach that of surgery or injection.[4].

A study comparing radiofrequency and HIFU (both applied below the skin surface) for neck sagging found no difference in improvement at 90 days.[9] At 180 days, the radiofrequency group showed lower sagging severity.[9] However, this was a specialized technique applied from below the skin, and our references do not include direct comparisons of XERF and HIFU.

A review of HIFU research also found maximum follow-up of 12 months.[9] Durability beyond that is not yet well understood.

What should I watch out for regarding pain and side effects?

Most are mild and temporary.[10] However, serious complications are reported more often with monopolar devices (2.6%) than bipolar devices (0.8%).[10].

HIFU pain averaged 4.3 on a 10-point scale.[9] In a survey of South Korean dermatologists, the most commonly cited HIFU side effect was fat loss (fat atrophy).[6] If you naturally have hollow cheeks, it is reassuring to discuss this concern in advance.

If you have metal plates or similar implants in your face, you must disclose this. Radiofrequency sends electrical current, so metal can become hot; HIFU ultrasound does not generate electrical current in metal.[11].

Which should I choose? A guide when you are undecided

Which is right for you depends on the degree of sagging (skin laxity) and fat distribution.[6] The general guidelines are as follows:

Skin firmness or fine lines of concern: XERF shallow mode or bipolar radiofrequency[1][6]

Jowling or jawline laxity of concern: XERF deep mode or HIFU[1][8]

Acne scars or surface irregularities of concern: Microneedle RF[6]

Metal implants in the face: Disclose to provider before radiofrequency treatment[11]

Severe sagging (skin laxity): Compare surgery and injection options in addition to devices[4]

Whether your sagging (skin laxity) can be adequately treated by a device alone, and how much fat you have, cannot be determined from reading alone. During consultation, have your sagging (skin laxity) degree and fat volume examined, and check whether the presence of facial metal is confirmed, so that you can confirm which mode or device is appropriate for you.