According to the National Institutes of Health, poly-L-lactic acid is “an absorbable, semi-permanent, injectable implant that can gradually restore volume and stimulate collagen formation. It works in two ways. First, there is the initial response to the injection, which is temporary but immediate due to slight swelling and fluid build-up. Second, there is the long-term effect as the carrier is absorbed, leaving behind just poly-L-lactic acid particles. These create an inflammatory response through phagocytosis by tissue macrophages, which breaks down the particles into absorbable elements and triggers collagen production. It takes roughly six months for 50% of the material to be absorbed, but the proven duration is usually between 12 and 24 months, with some patients experiencing longer-lasting effects before requiring another round of injections.