Etiology of Delayed Inflammatory Reaction Induced by Hyaluronic Acid Filler

Delayed edema, also known as a delayed inflammatory reaction or delayed-type hypersensitivity reaction, refers to symptoms accompanied by inflammation that occur 2–3 weeks after injection. Interest in this condition has increased worldwide owing to the emergence of the coronavirus disease (COVID-19) pandemic. Systemic changes occur when infected with the COVID-19 virus or when vaccinated, and delayed inflammatory reactions have been reported in individuals who previously received hyaluronic acid fillers. Therefore, it is expected that the patient’s condition will have a significant impact; however, the exact cause has not yet been described. This chapter provides a detailed description of possible causes of delayed inflammatory reactions.