The incidence of adverse events after hyaluronic acid filling is gradually increasing. In addition to acute reactions in the early postoperative period, there have been some cases of delayed inflammatory reactions. However, such events are rarely reported in Asia, which may be due to atypical symptoms, long intervals, and misidentification of the product quality. Herein, we present a case in which erythema of the neck appeared three weeks after hyaluronic acid injection into the neck lines and a delayed inflammatory reaction was diagnosed. Watchful waiting was performed, and the erythema subsided spontaneously after two weeks. This case suggests that in patients with a history of hyaluronic acid injections who develop allergic and inflammatory reactions after an interval, it is important to consider whether the reaction is a delayed inflammatory reaction, and if aggressive intervention is necessary.