## 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.