In Europe and the UK, there are over 200 brands of hyaluronic acid fillers, with various physical properties like lifting capacity, firmness, longevity – hence we use different fillers for different parts of the face. Facial fillers are medical devices. We must be diligent in infection control/ asepsis during these procedures.
So, the answer to this question is: “it depends”: You could have the most premium filler injection in less than ideal hygiene conditions – and cause infection, inflammation, nodules. The injection procedure may have been aseptic, but some aspect of your medical history may make you more susceptible to inflammation and filler reactions.
So, it is more to do with choosing the correct type of filler for that part of the face, and that patient (medical history), and whether it was placed with aseptic technique in the correct layer of the facial skin. (I did say “it depends”).
When you do your own research:
You are probably correct in thinking you should do your own research and learn as much as you can about the process, before choosing a doctor to manage your treatments. And that applies to all medical treatments, not just botox or filler injections. It is preferable for the doctor to be thinking as hard about the treatment as you are, and a good bit more when it comes to risk assessment and safety.
Reputable filler manufacturers would have already done research on inflammatory properties of their fillers, as part of the manufacturing and approval process.
The R&D process is rigorous, and in order to get approval, those fillers have to be proven to be consistently safe and effective. Galderma and Allergan (Restylane and Juvederm manufacturers) have decades of research backing their products. So, they are already able to advise us, who use their products, as to what we can do to keep our patients safe.