High-Intensity Focused Ultrasound Technology: Physical Principles, Biological Effects, and Clinical Applications in Facial and Neck Rejuvenation

High-Intensity Focused Ultrasound (HIFU) has emerged as a revolutionary non-invasive technology in aesthetic medicine, enabling targeted tissue remodelling and skin rejuvenation through precise thermal and mechanical effects. This narrative review provides a comprehensive examination of the physical foundations of HIFU, including acoustic wave propagation, piezoelectric energy conversion, and transducer design. It also explores its biological mechanisms, including collagen denaturation, neocollagenesis, fibroblast activation, and extracellular matrix remodelling. Clinically, HIFU has shown significant efficacy in improving skin laxity, reducing wrinkles, and enhancing facial and neck contours, with a favourable safety profile supported by multiple studies. The review also examines the limitations of conventional HIFU devices and describes the newest emerging multi-transducer platform with multi-depth cartridges and dynamic applicators. Key gaps in the literature include the scarcity of randomised controlled trials, limited data on higher Fitzpatrick skin phototypes, and the lack of standardised treatment protocols. By synthesising current evidence, this work positions HIFU as an established modality in aesthetic dermatology. A multi-transducer HIFU platform is discussed as a technically interesting emerging platform whose proposed advantages in precision, homogeneity, and comfort remain to be confirmed by independent comparative and randomised studies.