A Systematic Review of the Literature of Delayed Inflammatory Reactions After Hyaluronic Acid Filler Injection to Estimate the Incidence of Delayed Type Hypersensitivity Reaction.

Background: Hyaluronic acid (HA) dermal filler injection is believed to be a safe procedure. However, with the increase in the number of performed procedures and indications, the number of product-related complications, especially delayed inflammatory reactions, has also increased. Delayed-type hypersensitivity (DTH) reaction is one of these delayed inflammatory reactions, which is preventable by performing a pretreatment skin test.