Poly-D,L-Lactic Acid Filler Restores Hair Thickness and Shine by Ameliorating Age-Associated Follicular Decline

Hair aging, a complex physiological process involving progressive hair thinning and loss of luster, is primarily driven by functional decline of hair follicle components and sebaceous glands due to cumulative oxidative stress. This decline manifests as dermal papilla cell (DPC) senescence, with reduced insulin-like growth factor-1 (IGF-1) secretion, impaired hair matrix keratinocyte proliferation, and decreased keratin synthesis. We investigated the restorative potential of poly-D,L-lactic acid (PDLLA) filler, a biostimulatory polymer with antioxidant properties, against these age-related changes. PDLLA filler treatment significantly reduced oxidative stress-as indicated by decreased 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels-in hydrogen peroxide-induced senescent human DPCs, alleviated cell-cycle arrest, and significantly upregulated IGF-1 secretion. Conditioned medium from PDLLA filler-treated DPCs stimulated proliferation and pan-keratin expression in senescent hair follicular keratinocytes (HFKs). Intradermal PDLLA filler injection in aged mice significantly reduced 8-OHdG levels, restored DPC proliferative capacity (indicated by proliferating cell nuclear antigen [PCNA] positivity), increased IGF-1 expression within the dermal papilla, and enhanced HFK proliferation in the hair matrix. Consequently, PDLLA filler treatment robustly upregulated hair cortex keratins (K35, K85) and inner root sheath markers (AE15, K25, K71), leading to improved cuticle integrity and the attenuation of follicular miniaturization. Senescence within sebaceous glands was also mitigated, as evidenced by increased PCNA and peroxisome proliferator-activated receptor gamma (PPAR-γ) expression, accompanied by enhanced hair shaft reflectivity and shine. Overall, PDLLA filler ameliorated senescence-associated phenotypes and restored senescence-associated functional decline, supporting its potential as an intervention for age-related hair thinning and quality deterioration.