The side effects of hyaluronic acid injection are mainly in vascular embolism, local infection, local skin unevenness, swelling and so on. 1. Vascular embolism: if hyaluronic acid and other filler materials are injected into blood vessels, forming vascular blockage, the corresponding blood vessels will be necrotic due to ischemia and hypoxia, which will lead to more serious problems, such as blindness, stroke and so on. 2. Local infection: Hyaluronic acid injection is an invasive operation, improper sterilization may lead to bacterial infection. 3. Localized skin unevenness: Uneven amount of hyaluronic acid injection or wrong level of injection will lead to localized skin unevenness. 4. Swelling: Generally, mild swelling occurs within 2 hours after hyaluronic acid injection, peaks in 20 hours, and begins to subside after 70 hours, and the swelling is mostly temporary and can subside by itself. There are other side effects of playing hyaluronic acid, it is recommended to choose a compliant medical institutions, operated by professional doctors, side effects should be timely to the hospital.