DELAYED INFLAMMATORY REACTIONS AFTER DERMAL FILLERS: THE ROLE OF BIOFILM, IMMUNOLOGY, AND ANTIBIOTIC STEWARDSHIP

Dermal fillers have seen a marked increase in use over recent decades, becoming integral to both aesthetic and reconstructive medical practice. Although generally considered safe, delayed inflammatory reactions (DIRs) have emerged as clinically significant complications, exhibiting heterogeneous presentations and complex pathogenesis. This review provides a comprehensive analysis of the mechanisms, clinical features, diagnostic strategies, and treatment approaches associated with DIRs following dermal filler injections. The present review is grounded in a structured analysis of current scientific literature, with particular emphasis on immunological mechanisms, biofilm formation, and clinical management of delayed complications. Available evidence indicates that DIRs arise from multifactorial interactions between filler-related properties, host immune responses, and microbial factors. Biofilm formation plays a central role by enabling bacterial persistence, resistance to antimicrobial therapy, and chronic low-grade inflammation. Concurrently, immune-mediated processes—including foreign body reactions, delayed-type hypersensitivity, and adjuvant-like effects—contribute to the diversity of clinical manifestations. Clinically, DIRs may present as nodules, granulomas, abscesses, edema, or induration, with a delayed, often recurrent onset. Accurate diagnosis requires integration of clinical evaluation, imaging modalities such as ultrasonography, and, when necessary, microbiological or histopathological assessment. Treatment is based on a stepwise approach combining antibiotic therapy, hyaluronidase administration, corticosteroids, and, in selected cases, surgical intervention. In summary, DIRs constitute complex complications that require individualised management strategies. Enhanced understanding of biofilm-related mechanisms and immune responses is essential for optimising prevention, diagnosis, and treatment. Further research is warranted to standardise diagnostic criteria and develop evidence-based therapeutic protocols.