A Case Series of Rare Long-Term Bruising Following Injection of Liquid-Form Polycaprolactone: Mechanisms and Therapeutic Insights

Post-procedural bruising is one of the most common complications of aesthetic injections. Liquid-form polycaprolactone (PCL) is generally considered safe, with only transient and self-limiting adverse events reported. While bruising after liquid-form PCL injections is typically short-lived and no cases of permanent bruising have been documented, some patients may experience bruising persisting for several months. To date, however, no published reports have described such long-term cases. Here, we present retrospective review on seven clinical cases of persistent bruising following liquid-form PCL injections to the infraorbital, puncture point, and upper arm regions, and summarize their clinical management. Therapeutic approaches included pigment fragmentation (PICO, Nd:YAG, IPL, PDL), thermal loosening of the scaffold-tissue complex (radiofrequency, high-intensity focused ultrasound, warm application), mechanical dispersion (microcurrent stimulation, ultrasound, normal saline washout, gentle massage), and enzymatic degradation (hyaluronidase, lipase). All patients ultimately achieved resolution, and no serious adverse events were observed. These findings suggest that long-term bruising, although rare, is clinically relevant and may be associated with dense liquid-form PCL scaffold entrapment of pigment molecules or a Tyndall effect. Importantly, this phenomenon is not permanent, as its resolution parallels scaffold degradation over time. Preventive strategies, combined with multimodal management tailored to the underlying mechanisms, may reduce patient discomfort and optimize aesthetic outcomes.