The prior responses about the HA being natural and thus highly unlikely to cause a reaction are spot on. But if you are concerned, you could ask for a patch test. Be prepared to spend a lot though as they will have to use a new syringe of filler, and apply a tiny amount, and then wait a day or so. Most practices do not like to keep unused filler around: there are issues with contamination, loss of efficacy, etc. In other words, you may have to buy an entire syringe worth of filler for a test that is very very very unlikely to show you have an issue. But it is possible.
