I am always extremely itchy for weeks after the injection of any hyaluronic acid products. It's not a frank allergic reaction; rather, it's just persistent pruritis. It usually calms down after about 6 weeks or so. What causes that?
I have to say that is quite rare, rare to the point that we do not test for allergic reactions prior to an HA injection. I would suggest taking an antihistamine starting the day before you receive another injection and continue for 5-7 days, and see if that can control the issue. It has been reported in the medical literature but the number of allergic reactions compared to the number of people injected is very small