From Contouring to Rejuvenation: A Nationwide Big-Data Analysis of Hyaluronic Acid Injection Trends in Japan

<b>Background</b>: Hyaluronic acid (HA) injections have become a cornerstone of minimally invasive aesthetic medicine. While the demand for these procedures continues to grow globally, large-scale longitudinal analyses of patient demographics and specific injection site trends remain limited, particularly in Asian populations. Existing data in Japan are largely confined to aggregate procedure numbers. This study aimed to elucidate the transition in patient demographics and site-specific treatment trends using a nationwide big-data approach. <b>Methods</b>: This retrospective study analyzed 299,413 treatment sessions (417,590 injection sites) from patients who underwent facial HA injections at 110 clinics across Japan between October 2020 and December 2024. Data were analyzed by year, patient age, and injection site to evaluate demographic shifts and treatment patterns. <b>Results:</b> The annual number of treatment sessions increased steadily during the study period. A significant demographic shift was observed: while patients in their 20s were predominant in 2020-2022, the proportion of patients aged ≥ 40 years increased markedly from 2023 onward, accounting for more than half of all cases (63.7% in 2024). Treatment preferences varied distinctly by age; younger patients favored localized contouring (e.g., pretarsal fullness, chin), whereas older patients required multi-site rejuvenation. By 2024, the orbital rim became the most frequently treated site (22.6%). Statistical analysis confirmed that age was a significant predictor for multi-site treatments (<i>p</i> < 0.001). <b>Conclusions</b>: This large-scale analysis reveals a clear transition in the Japanese aesthetic market from contour enhancement in younger demographics to anatomy-based rejuvenation in middle-aged and older populations.