The most frequent side effects are mild and transitory: edema (slight swelling), redness in the treated area, hematomas or sensation of small subcutaneous nodules may appear, which generally disappear within a few hours to a few days. In patients with a history of cold sores there is a possibility of reactivation of the virus, which is prevented with appropriate medication. In rare cases, allergic reactions or infections may occur. If complications occur, hyaluronidase, an enzyme that dissolves HA safely and quickly, can be applied.