###### Abstract
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.