LAUSR

BACKGROUND Delayed-onset reactions are increasingly relevant given the growing use of hyaluronic acid dermal fillers. There is poor understanding of the phenomenon's etiology and incidence. OBJECTIVE To highlight differences between the dermal filler products with an emphasis on delayed-onset reaction incidence, pathogenesis, prevention, and treatment. METHODS A literature review was performed for delayed-onset reactions following hyaluronic acid dermal filler injection using PubMeb and Embase. Articles were included based on relevance, quality, and the predetermined definition of “delayed-onset reaction” (>30 days post injection). A total of 28 studies were included in the data analysis. RESULTS A total of 13,136 subjects from 28 studies treated with 15 filler types were included in the analysis. VYC-15L dermal filler injections carried the highest risk of delayed reaction with a mean incidence of 3.83% (n = 46/1,202), followed by VYC-20L (0.92%) and VYC-17.5L (0.88%). The mean incidence of delayed reactions among all filler types was 1.13%. CONCLUSION Incidence of delayed reaction to hyaluronic fillers ranges from 0% to 3.83% (mean = 1.13%) and varies by filler type. The exact etiology of these delayed reactions remains disputed. Future studies should report reaction description, precise timeline, and posttreatment immunologic history to better delineate the incidence of delayed-onset hypersensitivity reactions.