Restylane is actually FDA approved. I've read up about it. Mostly there could be swelling and bruising upto two weeks after the Restylane filler injections to eyelids or cheeks. Sometimes you get lumps which have to be dissolved with hyaluronidase. You can also get actually dangerous or painful allergic reactions.

The products are well tested but there are concerns. I read about a number of reactions, this is after all injecting stuff into the delicate skin on your face. So people usually have some pain for about a fortnight till it settles down, and even then they can have had uneven effects, allergies, reactions, sometimes quite serious.