This is a hot topic right now because there is a synergistic aspect to combining various treatments well.  The problem is that there are virtually no studies at all on combining  treatments so I have to rely on the few studies out there, my experience and the experience of many of my collegues.   I usually have my patients wait 3-7 days after a Thermage or 7-14 days after Fraxel to do injections like Sculptra or Juvederm.  There's no absolute magic to those numbers but since I'm using Sculptra or Juvederm to contour the face, I like to have all the swelling gone so I can be very accurate in my placement.   It's also nice to have the outer layer (epidermis) healed after the Fraxel so I'm not injecting through already irritated, healing skin. Hope that helps.  Dr. I