In most cases, Hyaluronic Acid proves to be a safe ingredient, but it is known to cause certain allergic reactions in some people including but not limited to -
redness
itching
swelling
Hence, it is strongly recommended to do a skin patch test before introducing hyaluronic acid serum into your skincare regime.
In case of any aforementioned side effects, discontinue the use of the product. If the side effects do not subside within a week, make sure to get in touch with your dermatologist.