The other consultants have referenced the article, which suggests that Restylane induces the formation of collagen by causing swelling and subsequent recruitment of the cells responsible for collagen production. All of us who have been injecting hyaluronic acid products since they were released in 2000, have observed a "retention" of effect, especially in the lips, after repeated treatment. What is not clear is whether the collagen stimulated is Type I (desirable "de novo") or III (scar type) is unclear. Sculptra maintains that the type of collagen induced by their product is type I, which would be extremely unique and thus a truly anti-aging modality. I don't know what subtype collagen is induced by Radiesse. However the most important consideration for me, as a plastic surgeon, who may offer surgery to a patient is whether these injectables will disqualify patients from future surgeries, if they desire them in the future. I have successfully performed facial surgery on patients who had previously used HAs, Sculptra and not encountered problems with wound healing. Good luck.