INTRODUCTION
Hyaluronic acid (HA) filler injection is the second most commonly performed nonsurgical aesthetic procedure globally. HA filler use has risen sharply, driven by advantages over earlier collagen-based fillers, such as limited immunogenicity, reduced migration after injection, longer duration of effect, and ease of use.1 While HA fillers have a well-established long-term safety profile, recent United States Food and Drug Administration (FDA) updates have strengthened warnings about delayed-onset inflammation near injection sites, prompting increased concern from patients and clinicians.2-4
Complications arising from HA filler procedures are generally categorized as early or late reactions.2 Early reactions occur within 14 days of the procedure and may include bruising, hives, itching, swelling, or allergy, including anaphylaxis.2,5 Early complications are typically minor and caused by the injection technique or the normal inflammatory response.1 Delayed complications are broadly defined as those occurring ≥14 days postprocedure.2 Importantly, definitions across guidelines vary for what is considered "early" or "late,"1 and others categorize reactions based on type (ie, allergic or hypersensitivity reactions [early] vs immune-mediated reactions [delayed]).5-7 The true incidence of delayed-onset reactions is difficult to determine,
Complications arising from HA filler procedures are generally categorized as early or late reactions.2 Early reactions occur within 14 days of the procedure and may include bruising, hives, itching, swelling, or allergy, including anaphylaxis.2,5 Early complications are typically minor and caused by the injection technique or the normal inflammatory response.1 Delayed complications are broadly defined as those occurring ≥14 days postprocedure.2 Importantly, definitions across guidelines vary for what is considered "early" or "late,"1 and others categorize reactions based on type (ie, allergic or hypersensitivity reactions [early] vs immune-mediated reactions [delayed]).5-7 The true incidence of delayed-onset reactions is difficult to determine,
