Immediate nor delayed type hypersensitivity plays a role in late inflammatory reactions after hyaluronic acid filler injections

Purpose: The exact etiology of late inflammatory reactions (LIRs) to hyaluronic acid (HA) fillers is currently unknown. Some argue that these result from a hypersensitivity reaction, although evidence to support this is very scarce. Most reports on such reactions are not substantiated by positive skin tests. The purpose of our study was to determine whether immediate or delayed type hypersensitivity reaction follows hyaluronic acid (HA) filler injections. Patients and Methods: Twelve patients were referred for general allergic screening (patch tests), as well as specific intradermal testing (injection of 0.1cc boluses) on the medial upper arm with a selection of several currently available hyaluronic acid (HA) fillers on the market. A positive allergic reaction was defined as erythema, firmness or swelling. Results: During the 4 month follow-up, no reactions to any of the tested HA fillers were reported. No correlation was found between results from the general allergic screening and a history with LIRs to HA fillers. Conclusion: The results suggest that neither type I nor type IV hypersensitivity plays a role in late inflammatory reactions (LIRs) to hyaluronic acid (HA) fillers.