Distinct Regenerative Mechanisms of Calcium Hydroxyapatite and Poly-L-Lactic Acid in Skin Biostimulation: A Systematic Review of Biological Pathways and Clinical Outcomes

Although calcium hydroxyapatite (CaHA) and poly-L-lactic acid (PLLA) are widely used as injectable biostimulatory agents, their biological mechanisms of action are heterogeneously reported and often described in broad clinical terms. To date, no review has comprehensively compared the cellular and molecular pathways underlying CaHA- and PLLA induced skin biostimulation. Clarifying whether these agents promote true regenerative processes and delineating their distinct biological pathways is essential to improve mechanistic understanding and support evidence-based clinical use.