Complications and Risks of High-Intensity Focused Ultrasound (HIFU) in Esthetic Procedures: A Review

Abstract

High-intensity focused ultrasound (HIFU) is a non-invasive technology widely used for facial and body rejuvenation, skin tightening, and fat reduction. It stimulates collagen production and induces apoptosis in fat cells, offering an effective alternative to surgical procedures with minimal downtime and reduced recovery periods. As a result, HIFU has become an increasingly popular choice for patients seeking non-surgical esthetic enhancements. A comprehensive literature search was conducted using PubMed, Scopus, and SpringerLink to assess HIFU-related complications. Twenty-two studies published between 2010 and 2025 were identified, all involving female participants. The findings confirm that HIFU is generally safe and effective, with most complications being mild and transient, such as temporary erythema, swelling, and discomfort. These side effects typically resolve within a few hours to days without requiring medical intervention. However, rare but significant complications like fat atrophy, nerve irritation, and hyperpigmentation have been linked to improper device settings, inadequate practitioner expertise, and insufficient patient assessment. Ensuring proper training, adherence to standardized treatment protocols, and individualized patient evaluations can significantly minimize these risks and optimize patient outcomes. Long-term follow-up studies and further research on standardized safety protocols, optimal energy settings, and patient selection criteria are essential for enhancing the effectiveness, predictability, and safety of HIFU in esthetic medicine.

1. Introduction

The continuous advancement of technology in the field of esthetic procedures has led to the development of numerous applications that contribute to the restoration and improvement of various issues affecting skin and fat tissue. These technological innovations include modern, non-invasive devices that operate based on the generation and transmission of ultrasound energy. The ultrasound technologies used to tighten and rejuvenate the skin in a non-invasive way are high-intensity macro- and micro-focused ultrasound (HIFU). The choice between the two depends on the patient’s esthetic problems [1].

Ultrasound consists of sound waves at frequencies too high for the human ear to detect (>16 kHz). Ultrasound is used in medicine for diagnostic and therapeutic purposes. Ultrasound devices used for diagnostic purposes emit frequencies from 1 to 20 MHz, while ultrasound devices such as HIFU emit frequencies of 0.8–3.5 MHz. Also, the energy emission levels of HIFU are considerably higher than those of diagnostic ultrasound. The ultrasonic waves of HIFU devices focus on the target tissue for therapeutic action, e.g., the removal of neoplasms, with little to no effect on the surrounding tissue. The oldest and most popular clinical application of HIFU is the removal of prostate cancer. It is also used for uterine fibroids and the removal of bone metastases, as well as in other organs. One of the most recent HIFU applications is tattoo removal [1,2].

HIFU is used as an esthetic procedure and is a contemporary, non-invasive treatment technique that has been proven to effectively minimize fat accumulation while simultaneously improving skin laxity [2]. The most important non-thermal mechanism of tissue disruption using HIFU is acoustic cavitation, which causes local destruction of the targeted tissues due to the high pressures and temperatures caused by cavitation. The fundamental operating principle of this technology is the conversion of mechanical energy into thermal energy. The energy that is generated at specific focal points within the tissue can induce the denaturation of tissue components, such as collagen. This process leads to tissue remodeling and assists in restoring the structural integrity of the treated areas [3]. Studies have demonstrated that ultrasound can be selectively and deeply absorbed by tissues, in a controlled manner, making it highly efficient for esthetic problems [4].

The headpieces of HIFU are specialized and are applied directly to the surface of the skin using a conductive ultrasound gel. The gel ensures optimal transmission of ultrasound waves to the appropriate depth for effective treatment. These headpieces are equipped with probes that can penetrate different depths within the skin, including 1.5 mm, 3 mm, 4.5 mm, 6 mm, 8 mm, 13 mm, and 16 mm. HIFU treatment has the advantage of penetrating deeper into tissues than other non-invasive technologies used for esthetic procedures [1]. Despite penetrating so deeply, the procedure is non-invasive because it does not cause any injury or irritation to the epidermis [5]. The main mechanism of HIFU is to convert acoustic (mechanical) energy into thermal energy and, as a result, to create biological effects in the dermis, superficial myoaneurotic system (SMAS), and fat tissue. Focusing high-energy ultrasound causes a temperature increase of 65–75 °C at microscopic points in different layers of the skin, depending on the target tissue and the esthetic problem. When the temperature in the dermis is above 42°, the fibroblasts begin to produce collagen. The focused points that are heated using HIFU are named thermal coagulation points (TCPs) and at these points, due to the coagulation temperature, collagen denaturation and contraction occur. The process of reaction and repair of the wound then begins, without causing damage to the surrounding tissues [4,6]. This thermal damage triggers a wound-healing response, resulting in the production of collagen and elastic fibers. The skin becomes thicker and more elastic, due to the creation of shorter and thicker collagen fibers. This is caused by the breaking of intramolecular hydrogen bonds, which forces the collagen chains to fold and be more stable. So, the human body itself enters the process of reversing aging in a natural way. The basic principles of HIFU technology are the death of cells and volume reduction in the selected treatment area through coagulation, leading to tissue shrinkage and tightening as a result. Also, HIFU may have an impact on melasma (a photoaging disorder of the skin), eliminating melanin and pigment residues [1].

The duration of each HIFU session depends on the specific body area being treated and the extent of the esthetic problem. On average, a single session lasts between 60 and 90 min [5]. The procedure can be repeated up to four times per year. However, in cases where ultrasound transmission is directed at a depth of 4.5 mm (SMAS layer), repeated applications are strictly prohibited for at least six months following the previous session. This precautionary measure is necessary to prevent the risk of lipoatrophy, as frequent applications within short time intervals could lead to unintended complications [1,5].

The ultrasound energy emitted during treatment stimulates the production of new collagen through a thermal activation process. Micro-focused ultrasound with visualization (MFU-V; Ulthera^® System, Merz North America, Raleigh, NC, USA) was approved by the U.S. Food and Drug Administration in 2009 for brow lifts. Then, approval for neck and submandibular lifts, facial and upper chest rejuvenation, skin whitening, hyperhidrosis, acne, and lipolysis followed [6,7]. Micro-focused followed [6,7] Microfocused ultrasound (MFUS) technology allows precise targeting at specific depths, making it ideal for delicate areas such as the eye contour [6]. Since then, numerous clinical studies have reported that HIFU/MFU-V devices are effective treatments for skin tightening, wrinkle reduction, and reducing adipose tissue, but Ultherapy’s real-time imaging (MFU-V) offers greater accuracy and safety. There are many HIFU devices on the market and some of them have a built-in cooling system.

HIFU is one of the non-invasive technologies that we teach to our students at the University, and we want to know both its benefits and complications. Our aim for this review was to collect all the studies that have recorded complications from HIFU so as to fill the gap we encountered in the literature, which was the concise review of complications from HIFU for the esthetic purposes. It is important for both students and healthcare professionals who implement this technology to be aware of all possible complications and to inform their patients about the mildest to the most dangerous adverse effect. To ensure safe and effective HIFU application, candidates should not belong to any of the contraindicated categories. Firstly, HIFU treatment should never be applied to restricted areas, as improper use may lead to unwanted side effects. The non-permissible areas include temples, eye sockets, and levator labii superioris (LLS) muscle (applying HIFU here may cause reversible facial nerve paresis, with recovery occurring within 2–3 weeks) [1].

According to the latest scientific data, contraindications for HIFU in esthetic procedures are classified into two main categories: (a) absolute and (b) relative contraindications. The following conditions are strict contraindications for HIFU, as treatment could cause severe adverse effects: (a) dermal implants, (b) presence of pacemakers or metal implants (e.g., metal clips from brain surgery, an implanted defibrillator, or any other medical device), (c) pregnancy and breastfeeding, (d) active skin infections or inflammation, (e) cystic acne, (f) severe or unstable medical conditions, including certain cardiovascular or auto-immune diseases, coagulation disorders, use of anticoagulant and antiplatelet medications, epilepsy, active vitiligo, febrile conditions (fever), uncontrolled liver disease or diabetes, severe psychiatric disorders, a history of severe allergies, and silicone implants [3,8,9]. The relative contraindications are the following: (a) individuals under 25 years of age, (b) individuals over 60 years of age, (c) recent facelift or laser rejuvenating treatment (within the past 12 months), (d) smokers and individuals with photoaged skin, as their skin may have reduced healing capacity, (e) excessive skin laxity, and (f) Body Mass Index (BMI) > 30, as increased skin laxity and a high BMI may reduce HIFU effectiveness [3]. Also, the history of conditions affecting skin healing, including keloids, hypertrophic scars, and connective tissue diseases were included among contraindications [1,4].

2. Materials and Methods

A comprehensive and systematic literature review was carried out by searching three prominent scientific databases: PubMed, Scopus, and SpringerLink. For ensuring the methodological rigor and replicability for our narrative review, the SANRA checklist was used [7]. The objective of this search was to identify all peer-reviewed articles that discuss the potential complications and adverse effects associated with high-intensity focused ultrasound (HIFU) treatments when applied as an esthetic procedure. Eligible studies included randomized controlled trials, controlled trials, cohort studies, and case series. Objective and subjective outcomes were assessed. To ensure the most thorough collection of relevant studies, the search strategy was meticulously designed using a combination of specific keywords and phrases, including “HIFU in esthetics”, “rejuvenation”, “facial tightening”, “side effects”, “complications”, “risks”, and “contraindications”. These keywords were strategically chosen to capture a broad range of studies discussing both the efficacy and safety concerns related to HIFU applications.

In order to ensure inclusivity and the most extensive coverage of existing research, no restrictions were applied regarding language or the publication date of the studies. This approach facilitated the retrieval of the most up-to-date and historically significant research on HIFU technology in esthetic medicine. The review encompassed a wide spectrum of articles, including clinical trials, systematic reviews, case studies, and retrospective analyses that specifically focused on the complications, risks, and potential contraindications of HIFU procedures. Through this rigorous selection process, a total of twenty-two relevant studies published between 2010 and 2025 were identified for inclusion in the final analysis. These studies provided valuable insights into the side effects, complications, and limitations of HIFU in esthetic medicine. A notable observation was that all the selected studies involved female participants, highlighting a potential gender bias in the existing research. This finding suggests that additional studies involving male subjects may be necessary to gain a more comprehensive understanding of the effects and safety profile of HIFU across different populations.

To maintain the highest level of accuracy and relevance, studies that did not explicitly report complications, side effects, or potential risks associated with HIFU treatment were systematically excluded from the analysis. This ensured that only scientifically rigorous and directly relevant data contributed to the overall findings of this review. The inclusion criteria prioritized studies that offered quantitative and qualitative assessments of post-treatment complications, as well as those that provided clear documentation of patient outcomes following HIFU procedures. Also, there were some limitations of our review, such as heterogeneity in study designs, small sample sizes, a lack of long-term follow-up data, and an all-female patient population across these twenty studies.

3. Results

From the results of our systematic review, it appears that there are few studies (n = 22) assessing complications from HIFU treatment in esthetic procedures over a sixteen-year period. Of these studies, some reported one or two cases with rare complications and others reported more generally mild adverse effects that are transient and reversible, without, however, reporting the exact percentage of patients. From these few studies, we summarized all the mild and serious complications that have been recorded so far, and one of the first findings was that all patients who experienced complications did not have any particular characteristics, apart from more sensitive and dehydrated skin. However, all the studies had a shared characteristic in that the wrong diagnosis and application by the operator caused the complication.

Another result of this review was that none of the other HIFU devices (except micro-focused ultrasound with visualization) provide visualization or verification of reaching the superficial myofascial system. Although HIFU devices are marketed for indications similar to those of MFU-V, studies suggest that these indications are limited [8]. These studies with MFU-V/HIFU report that real-time visualization and the ability to detect coupling contribute to efficacy and prevention of complications. Features such as tight thermal regulation, large focal gain, and short beam length contribute to the safety and efficacy of HIFU application, but they were not collectively found in any of the HIFU devices, except for MFU-V. Careful selection of the parameters in HIFU devices (e.g., fluency, etc.) will minimize any adverse effects [6,8]. Only two of the twenty-two studies that were included in this review reported complications from MFU-V, which are analyzed in the following section. However, one of the major advantages of macro- and micro-HIFU treatment is the immediacy of initial results.

Studies have shown that the characteristics of the HIFU’s headpiece and the selected fluency (J/cm²) are the most important device parameters, and these will determine the outcome in skin or fat tissue. Many patients notice improvements in skin texture and firmness immediately after their first session. However, the full effects of the treatment unfold progressively over time due to the body’s natural wound-healing response and collagen remodeling. The most significant esthetic improvements typically become apparent between 90 and 180 days following the procedure [1]. The longevity of these results varies depending on individual biological responses, but in general, the benefits of HIFU treatment can last for up to 18 months [1,8]. A recent systematic review assessing the effectiveness of HIFU utilized the Global Esthetic Improvement Scale (GAIS) as a measurement tool. The findings from this review indicated that approximately 88% of patients who underwent HIFU treatment experienced some degree of visible enhancement in skin laxity and contouring [4]. Furthermore, studies suggest that HIFU is particularly well suited for non-obese individuals who are looking for a moderate yet noticeable reduction in localized fat deposits.

Compared to other non-invasive fat reduction technologies (e.g., radiofrequency, laser, cavitation, etc.), HIFU stands out as the only method capable of delivering substantial results after a single treatment session. In the United States, HIFU has received regulatory approval for fat reduction alongside other non-invasive procedures, including radiofrequency, low-level laser therapy, and cryolipolysis. However, among these techniques, HIFU remains one of the most widely regarded solutions due to its high efficacy and reduced likelihood of complications. Unlike traditional surgical interventions such as lipoplasty, HIFU treatments do not require anesthesia, incisions, or prolonged recovery periods. Early clinical data support the effectiveness and safety of HIFU for fat reduction and body contouring. Unlike radiofrequency, laser therapy, and injection lipolysis, which have been associated with various complications, HIFU demonstrates a lower risk profile while maintaining substantial efficacy [9,10].

Another recent comprehensive analysis of 843 HIFU applications found that this non-invasive treatment is both safe and effective in achieving a circumferential fat reduction of at least 2 cm in targeted areas such as the abdomen, hips, and thighs. Notably, the study concluded that no severe or long-term adverse effects were associated with HIFU treatment [4].

3.1. Safety and Effectiveness of HIFU Application in Esthetics

• Before undergoing high-intensity focused ultrasound (HIFU) treatment, it is of utmost importance that medical professionals conduct a comprehensive assessment of the patient’s medical history. This includes evaluating any previous esthetic treatments—whether they were invasive, such as surgical facelifts or liposuction, or non-invasive procedures like laser resurfacing, chemical peels, or radiofrequency therapy. A thorough understanding of the patient’s medical background helps in determining whether they are a suitable candidate for HIFU treatment while minimizing potential risks and complications.
• Once the patient is deemed appropriate for the procedure, healthcare providers must offer detailed and transparent information regarding every aspect of the treatment. This includes discussing the following:
• Contraindications for HIFU treatments: Medical professionals should clearly explain which conditions or medical histories make a patient ineligible for HIFU, such as active infections, certain chronic diseases, or previous treatments that could interfere with ultrasound energy absorption.
• Sensations that may be experienced during the procedure: Patients should be informed about the expected levels of discomfort during the application of HIFU. This can vary between individuals, with some experiencing mild tingling, heat, or slight discomfort, while others may report moderate pain that subsides quickly after treatment.
• Expected sensations immediately after the procedure: Right after the session, patients might experience mild redness, tenderness, or slight swelling in the treated area. These effects are generally temporary and subside within a few hours to a few days.
• Sensations and clinical appearance of the skin in the days following treatment: As part of the natural healing response, the skin may feel slightly tight, with mild swelling or tenderness persisting for a short period. Bruising may occur in some cases, especially in patients with more sensitive skin.
• Expected results, including the timeline for visible improvements and the duration of effects: Patients must understand that HIFU results are not instantaneous. While some initial tightening may be visible immediately, the primary benefits, such as collagen production and overall skin rejuvenation, take time to fully develop, with the most noticeable effects appearing within two to three months post treatment. The optimal results usually peak around the six-month mark and can last up to 18 months, depending on individual skin characteristics and lifestyle factors.
• Pre-treatment and post-treatment care instructions: Clear guidelines should be provided on how to prepare for the procedure (e.g., avoiding direct sun exposure, discontinuing the use of certain skincare products, staying hydrated) and what steps to follow afterward (e.g., using gentle skincare, applying sunscreen, avoiding excessive heat exposure, and refraining from aggressive exfoliation or chemical treatments).
• Recommended frequency of HIFU treatments: Patients should be advised on how often they can safely undergo HIFU procedures. Generally, one session provides noticeable improvements, but additional treatments may be recommended at intervals of six months to a year, depending on the area treated and the patient’s esthetic goals.
• Potential side effects associated with the procedure: While HIFU is generally considered a safe and effective non-invasive treatment, patients should be aware of potential minor side effects, including temporary redness, mild swelling, or tingling sensations in the treated area. Rare complications such as prolonged numbness or bruising should also be discussed [4,5,6,9].

In addition to thoroughly explaining these aspects, obtaining informed consent from the patient is a crucial step before proceeding with treatment. A signed consent form ensures that the patient fully understands the procedure, its expected outcomes, and any associated risks. To further enhance documentation and track progress, it is advisable to take before-and-after photographs at multiple intervals, particularly at two and six months post treatment. These images serve as a valuable tool for assessing the effectiveness of the procedure, managing patient expectations, and ensuring transparency in results. The following table (

Table 1. Basic prerequisite for safe and effective HIFU application. (Modified by Dr. F. Biskanaki, 2025).

Category	Requirements
Personal History	The patient should not belong to any contraindicated categories.
Professional Expertise	Adequate knowledge and experience in the use of HIFU devices for facial and body esthetic procedures.
Diagnosis	Accurate diagnosis of the case and discussion with the patient to ensure they have realistic expectations and understand the expected results.
Device	The HIFU device should be reliable, properly maintained, and correctly adjusted according to the protocol for each device. The selection of the appropriate headpiece should consider factors such as skin type, hydration levels, age, and the specific esthetic concern.
Application	Proper pressure of the handpiece on the skin, sufficient use of ultrasound gel, and avoidance of non-permissible areas (temples, eye sockets, and the levator labii superioris (LLS) muscle) must be ensured. Avoid applying HIFU multiple times to the same spot. Follow appropriate time intervals between sessions (e.g., a second HIFU treatment using the 3 mm headpiece may be performed three months after the first treatment).
Patient Instructions	Clear pre- and post-treatment guidelines should be provided.
Patient Cooperation	The patient must follow all pre- and post-treatment instructions to maximize results and minimize risks.

) summarizes the essential conditions that must be met to ensure the safe and effective application of HIFU in esthetic procedures [1,3,10].

Additionally, after the procedure, there should be no visible burns, extreme redness, or permanent injury to the skin, and it should already appear firmer, slightly lifted, and healthier, without any visible irritation or prolonged redness. This highlights the safety profile and controlled nature of HIFU when performed by trained professionals under appropriate clinical conditions [11].

3.2. Side Effects of HIFU

Recent studies report that redness is the most commonly observed side effect, typically resolving immediately after treatment. However, if the device head is not applied with sufficient pressure or if an inadequate intermediate material (gel) is used, skin surface irritation may occur. Although this reaction is reversible, it indicates improper treatment application. Possible causes include the following:

• Insufficient contact between the device head and the skin;
• Inadequate amount of gel;
• Higher-than-recommended energy intensity.

Additionally, if the operator fails to avoid non-permissible areas (e.g., temples, eye sockets, or the depressor anguli oris muscle) and applies HIFU in these regions, it may lead to temporary facial nerve paresis.

During the procedure, patients commonly experience the following:

• A sensation of increased temperature on the skin;
• Mild pain, which is generally well tolerated;
• Mild redness in the treated area, which disappears immediately after the procedure.

Most studies have evaluated HIFU-related risks for up to 12 weeks post treatment. However, only one study has assessed safety and documented adverse events over a 24-week period [12].

HIFU side effects include mild-to-moderate discomfort, bruising (ecchymosis), and swelling (edema), all of which are transient and resolve naturally. No reports exist of scarring, burns, or clinically significant changes in lipid panels, inflammatory markers, renal function, or liver function [13]. Furthermore, no study has linked HIFU to any serious or permanent adverse effects [4].

However, when HIFU is performed correctly and all safety conditions are met, the likelihood of side effects or complications is minimal. The following table summarizes the most common complications and side effects associated with HIFU in esthetic procedures: (

Table 2. Complications of HIFU treatments in esthetic procedures (Modified by Dr. F. Biskanaki, 2025).

Category	Complications
Pain & Sensory	Pain, prolonged numbness [13,14]
Skin	Edema, erythema, bruising/purpura, hypopigmentation, scarring [9,15,16], cheek fat atrophy, atrophy, and/or cutaneous necrosis [17], significant scar tissue formation, swelling, paresthesia, and herpes simplex virus (HSV) outbreak [18].
Eyes	Potential ocular complications (raumatic cataract, visual impairment, and injuries to the iris and conjunctiva) [6].
Fat Tissues	Fat atrophy [19,20].

).

3.2.1. Skin Complications

MFU-V/HIFU devices are moderately painful and may cause transient erythema with or without edema. A recent review of sixteen studies (with a total of 337 patients) on the safety and complications of micro-focused ultrasound (MFU) reported rare adverse effects, including the following:

• Dysesthesia (numbness or hypersensitivity);
• Bruising and stinging;
• Mandibular burns;
• Striations (streak-like marks on the skin);
• Contact dermatitis [3].

Different device settings and treatment protocols can result in varying risks. Some studies have reported that edema, erythema, and pain are common on the first day after treatment, while hyperpigmentation may occur three months post-HIFU therapy [4]. In some cases, healthcare professionals may struggle to identify complications affecting the epidermis. Additionally, it can be challenging to determine why HIFU treatment has failed or why the skin appears worse than before.

Reports suggest that plastic surgeons often encounter difficulties when performing facelifts on patients who have previously undergone incorrectly applied non-invasive HIFU treatments. If tissue overheating occurs due to improper device settings, multiple passes on the same area, or inadequate time between energy-based treatments, complications may include the following: (a) cheek fat atrophy and (b) significant scar tissue formation [18].

A study combining HIFU with Botox and temporary and semi-permanent dermal fillers (within six months of treatment) reported seven adverse events:

• Bruising/purpura;
• Swelling;
• Paresthesia;
• Herpes simplex virus (HSV) outbreak.

Of these, only the HSV outbreak was attributed to the combined treatments [19].

3.2.2. Ocular Complications

Micro-focused ultrasound (MFU) technology allows precise targeting at specific depths, making it ideal for delicate areas such as the eye contour [6]. However, the HIFU/MFU treatment for eyelid rejuvenation has been associated with serious ocular complications [6]. This technology delivers focused high-energy ultrasound at 65–75 °C to TCPs, making the focused dots produce high temperatures as a result. It can achieve the tension and pulling effect of the deep dermis and fascia [1,6,9].

A recent published study reported that a 40-year-old female had mild pain and blurred vision in the left eye, accompanied by redness and discomfort. It was reported that she was followed up for one year. The treatment device was a high-intensity bundled ultrasound skin surgery instrument (SHURINK-A 50/60 Hz (A35100.02 (3)). After HIFU treatment, the vision in her left eye was blurred for the duration of half a day. The device settings were as follows: 0.9 J/cm², at a depth of 2.0 mm, double-line emission, with a line length of 20 mm and a distance of 1.5 mm between each TCP, and a distance of 3 mm between each row of lines. The woman reported a history of bilateral refractive surgery with laser in situ keratomileusis (FS-LASIK) performed one year prior. She reported that six months after HIFU application, she still had blurred vision in the left eye [6].

In another study, a 47-year-old woman (without any ophthalmological history) was reported to have symptoms of discomfort during HIFU around the right upper eyelid area. Thus, the left eyelid was not treated. HIFU was applied by a trained dermatologist and no eyelid protection was used. The patient immediately visited the hospital, where ophthalmologists reported that she had mild ocular hyperemia, three spots on her cornea, and three punctiform epithelium defects with stromal infiltrate and local stromal edema, alongside an adjacent clear cornea.

The intraocular pressure (IOP) was 16 mmHg, and the funduscopy showed no abnormalities. The patient was treated with eye drops in the first week and then tapered off until the completion of 30 days of treatment [6,18].

The ultrasonic energy generated by HIFU can denature proteins, leading to conditions such as the following:

• Severe traumatic cataracts leading to lens-related surgery;
• Visual impairment;
• Injuries to the iris (blurred vision and iris pigment detachment);
• Heat damage to the conjunctiva;
• Increased intraocular pressure (IOP);
• Rare cases of myopia.

Although there are studies that suggest that topical application of HIFU to the eyelids can denature the protein inside the lens, HIFU therapy is approved for use in the periocular area [6]. HIFU can denature proteins, leading to side effects such as the following:

• Severe traumatic cataracts leading to lens-related surgery;
• Visual impairment;
• Injuries to the iris (blurred vision and iris pigment detachment);
• Heat damage to the conjunctiva;
• Increased intraocular pressure (IOP);
• Rare cases of myopia.

Also, the HIFU probe should not be placed in the eyebrow arch and eyelid to avoid eye injury [6].

3.2.3. Traumatic Carotid Artery

A recent study reported that after HIFU application in a 41-year-old woman, the following symptoms appeared: headache and clinical manifestations of stroke. Magnetic resonance angiography (MRA) of the head and neck and computed tomography (CTA) revealed severe stenosis of the left internal carotid artery. The cause of the stroke in this woman was likely the application of HIFU.

The damage to adjacent tissues was probably due to the insufficient focal depth of the compression (specifically, it was 7D HIFU). Symptoms of stroke appeared within 6 months of the detection of severe stenosis of the carotid artery [5,20]. Therefore, the patient underwent left carotid resection. Better visualization systems and more rigorous operator training are required to reduce the risk of this complication [20].

3.2.4. Neurologic Complication

Neurologic complications from HIFU treatment are very rare. A recent study reported that a 49-year-old woman developed mild numbness around the perioral region at 7 days post HIFU treatment, but it resolved spontaneously within a month. Another complication that was reported was temporary numbness along the mandible, and it appeared in four of twenty-two participants. The precise mechanism of nerve injury after HIFU treatment for face and body rejuvenating is unknown, but it has been demonstrated that thermal energy, produced by HIFU on the superficial musculoaponeurotic system (SMAS), may cause injury to (facial) nerve branches distributed in the SMAS. HIFU technology can penetrate very deeply into tissues, to a point that could even lead to nerve injury. The marginal branches of the mandible and the temporal branches of the facial nerve are located superficially on the face. For this reason, the application of HIFU on the chin and forehead must be performed carefully and not aggressively. To achieve this, energy delivery settings must be selected correctly, and the head strokes must not be overlapped. Otherwise, overheating of the tissues will occur, leading to complications. Even if this side effect occurs, it is considered benign and resolves on its own [21].

4. Discussion

Completing this systematic review and facing difficulties such as heterogeneity, a lack of quantitative data, and limited references in the public literature, we tried to summarize all the complications that have been recorded so far from HIFU/MFU-V applications in esthetic problems.

The precursor to HIFU was micro-focused ultrasound (MFU) and both of them are non-invasive devices used as an esthetic procedure and demonstrate skin rejuvenating effects and body contouring [6,7]. Over the past decade, its popularity has grown significantly, owing to its ability to deliver measurable esthetic improvements without the need for surgical intervention [1,3,7]. HIFU is a procedure that relies on the application of ultrasound waves, which are precisely focused on a single point within the targeted tissue. The energy generated at these focal points results in a localized increase in temperature, leading to controlled thermal damage that triggers cell apoptosis, and through the denaturation and contraction of collagen, the induction of wound repair reaction [7].

The primary objective of this study was to examine complications associated with HIFU treatments as reported in the recent scientific literature, as well as to incorporate clinical experiences that can contribute to refining protocols and enhancing the safety and efficacy of HIFU applications [7,22]. Most of the studies concluded that no severe or long-term adverse effects were associated with HIFU treatment [4]. These findings reinforce the growing body of evidence supporting HIFU as a reliable and effective technique for esthetic enhancement.

There are many HIFU devices that have different parameter settings, which are crucial for the safety and effectiveness of applications. For example, the MFU-V device has the ability to visualize, an important characteristic that other devices do not have. Some other differences are the preservation of the patient’s history, the constant size and uniformity of the TCPs, and the precise localization of the energy concentration [7]. A notable finding from this review was that none of the other HIFU devices (except MFU-V) provide visualization or verification reaching the superficial musculoaponeurotic system. Also, only two of the twenty studies that were included in this review reported complications from MFU-V [6]. The other studies generally reported on HIFU devices and some complications that had been noticed between 2009 and now.

Patients undergoing HIFU treatments commonly report experiencing a range of sensations during and after the procedure. These include (a) pain or discomfort during application. Some individuals experience mild-to-moderate pain, typically described as a deep warmth or tingling sensation. This varies depending on the intensity of the treatment, the area being treated, and individual pain thresholds [21,23]. This symptom was reported in each study that is included in our review. (b) Immediately after HIFU treatment, the sensation is similar to internal bruising. This discomfort can last anywhere from 30 min to 10 days, with heightened sensitivity observed in individuals with more delicate or reactive skin types [1]. (c) Also, patients with dehydrated or sensitive skin may experience redness that can persist for approximately 30 min to several hours, depending on their skin’s response [3]. This is a normal reaction and usually resolves on its own without intervention.

Although HIFU is generally associated with minimal adverse effects, there have been few documented cases of serious complications, like carotid artery trauma [19]. HIFU technology is sometimes used for eyelid rejuvenation. However, it has been associated with serious ocular complications [6]. Previous studies have found that localized ultrasonic energy can denature the proteins inside the lens, resulting in lens opacity. Due to these risks, HIFU treatment near the eyes should be approached with extreme caution, because it can lead to severe eye conditions. However, it has been approved for treatment of the periocular area. Another complication of HIFU treatment is neurologic, which is very rare, benign, and self-resolving [21]. No study has linked HIFU with any serious or permanent adverse effects. The risk of adverse outcomes is significantly increased if the treatment is not performed according to established guidelines. Factors contributing to complications include the following: (a) incorrect device settings—if the ultrasound energy level is too high or improperly adjusted, it may cause excessive heating, leading to unintended tissue damage; (b) improper application techniques—the operator must have an in-depth understanding of facial anatomy to ensure precise placement of ultrasound pulses and avoid unnecessary exposure to sensitive areas; and (c) failure to adhere to established treatment protocols—HIFU is a technology-sensitive procedure, and deviations from standard treatment parameters can increase the likelihood of complications. Each esthetic procedure, whether invasive or non-invasive, presents its own set of benefits and potential risks. A key determinant of HIFU treatment safety is the expertise of the operator. Operators lacking adequate education, professional training, or specialized knowledge in esthetic medicine are significantly more likely to cause treatment-related complications. Ensuring that HIFU is performed by certified and experienced professionals is essential for reducing risks and optimizing treatment results [22,23].

Also, before a HIFU treatment, it is important that medical professionals conduct a comprehensive assessment of the patient’s medical history, obtain a signed consent form, and take before-and-after photographs at multiple intervals. These are valuable tools for assessing the effectiveness of the procedure, managing patient expectations, and ensuring transparency in results [1,3,9]. As previously mentioned the full transformative effects of HIFU do not appear immediately but develop gradually over a period of several months. By the two- to three-month mark, significant tightening and lifting effects should become noticeable, with final results reaching their peak by approximately six months after treatment.

In order to ensure optimal treatment outcomes and minimize risks, the following key factors must be considered: (a) careful selection of a reliable and approved HIFU device—using high-quality, clinically tested equipment is critical for maintaining consistency in treatment results and minimizing the likelihood of adverse effects; (b) precise parameter adjustments tailored to individual patient needs—since each patient has unique skin characteristics, adjusting the device settings according to the treatment area, skin thickness, and desired outcome is necessary for achieving optimal results; and (c) application of the procedure by highly trained and specialized professionals—proper execution of HIFU requires a strong understanding of skin physiology, ultrasound physics, and facial anatomy to ensure the accurate delivery of energy to targeted tissues [23]. Also, patients should wait an appropriate amount of time between esthetic treatments. If they have had Botox injections, a waiting period of at least three to four weeks is required. In cases of previous dermal filler treatments, the recommended interval is at least three to four months to prevent interactions between the ultrasound energy and the filler material. Products containing vitamin A derivatives, such as retinol and retinaldehyde, as well as high-concentration acids like glycolic and salicylic acid, should be avoided for at least three days before and three days after the procedure to prevent skin irritation, inflammation, or hypersensitivity. Excessive exposure to UV radiation, including direct sun exposure, sunbathing, and tanning beds, should be avoided for at least one week before the procedure. Even mild sunburn or skin irritation can increase sensitivity, potentially leading to redness and an elevated risk of complications following treatment [8,10]. The use of broad-spectrum sunscreen is essential to protect the treated skin from UV damage. Patients should avoid excessive exposure to heat sources, such as sunlight, tanning beds, hot baths, spas, and saunas, for at least two days following treatment. Prolonged exposure to intense heat from fireplaces, radiators, ovens, and hair dryers should also be minimized. It is important to encourage patients to maintain adequate hydration in the days leading up to treatment, as well-hydrated skin can improve the procedure’s efficacy and support faster recovery [1].

During HIFU treatment, the operator should continuously check in with the patient, ensuring that they are comfortable and responding well to the procedure. Immediate adjustments should be made if the patient experiences excessive discomfort [1,3,5]. While the procedure is generally well tolerated, some patients may experience discomfort or sensitivity. The use of local anesthesia is an option for individuals with hypersensitivity or low pain tolerance. As an alternative, the “talk anesthesia” technique may be used, which involves engaging the patient in conversation to distract them and reduce their perception of discomfort. This method has been found effective in alleviating anxiety and discomfort in many patients [1]. Post-treatment care plays a crucial role in ensuring the longevity of results and reducing the risk of complications. Patients should refrain from engaging in intense physical activities and strenuous exercise for at least several hours following the procedure, as increased circulation could exacerbate swelling or tenderness in the treated area. Patients should drink plenty of water post-treatment to enhance the effectiveness of the procedure and facilitate skin repair. Additionally, consuming an antioxidant-rich diet can aid in collagen production and skin regeneration.

By following these comprehensive pre-treatment and post-treatment guidelines, patients can optimize their HIFU experience, achieving maximum skin tightening and fat reduction benefits, and long-term results, with minimal risks. These make it a safer, more convenient alternative for individuals seeking a non-invasive face and body procedure [9].

Concluding this review, we have some suggestions for future studies, such as randomized controlled trials to evaluate the long-term safety and efficacy of HIFU. Also, comparative studies should be conducted on the application of HIFU with other invasive and non-invasive esthetic treatments, in order to indicate the correct intervals between treatments to avoid complications. Finally, we propose the construction of visualization devices such as the MFU-V for more safety and effectiveness.

5. Conclusions

In summary, high-intensity macro- and micro-focused ultrasound (HIFU) has established itself as a highly effective and minimally invasive technique for facial and body contouring, offering significant esthetic benefits with minimal pain and without recovery time [8]. Studies have consistently validated the safety and efficacy of HIFU for skin tightening, particularly in patients with mild-to-moderate skin laxity. However, in order to ensure optimal treatment outcomes and minimize risks, key factors must be considered, which we have reported [23].

Despite the growing body of evidence supporting HIFU’s effectiveness and safety, long-term follow-up data on its sustained results and potential long-term side effects remain limited. Also, there are no documented cases of delayed complications following repeated HIFU sessions [15,16]. Future research should focus on objective assessments of treatment outcomes. More controlled clinical trials using standardized evaluation criteria are needed to further validate the longevity and effectiveness of HIFU, and comparative studies with alternative non-invasive technologies (such as radiofrequency, microneedling, and laser) and injectables (Botox, PRP, etc.) could help refine treatment protocols. While short-term side effects are generally mild and transient, ongoing studies evaluating potential long-term complications or cumulative effects of repeated HIFU sessions will provide valuable insight into its overall safety profile [17].

With continued advancements in ultrasound technology, improved treatment protocols, and operator education, HIFU is likely to remain a cornerstone in non-invasive esthetic procedures, without complications [1].