Radiesse is not a gel filler in the way hyaluronic acid products are: The FDA labelling calls it "an opaque, sterile, non-pyrogenic, semi-solid, cohesive implant, whose principal component is synthetic calcium hydroxylapatite suspended in a gel carrier."
There are two components. They have two different jobs and two different fates.
Calcium hydroxylapatite microspheres, usually shortened to CaHA. These are tiny smooth spheres of a calcium-phosphate mineral. They are 25 to 45 microns across. That is far smaller than a grain of sand.
The gel carrier: It is made of sterile water, glycerin and sodium carboxymethylcellulose. That last one is a common thickening agent, usually written as CMC.
Radiesse (+) is the same implant with lidocaine added for comfort. The lidocaine versions were introduced through labelling supplements in 2015. The jawline indication belongs to Radiesse (+) Lidocaine specifically.
On the day of treatment, what you see is the carrier: The gel occupies space, so the treated area looks fuller straight away. A 2013 evidence review of calcium hydroxylapatite describes it as providing "an initial, immediate volume replacement for up to 12 months."
This is worth understanding, because it sets expectations in both directions. There is no waiting period before anything happens. That is different from some other collagen stimulators. But the thing you see on day one is not the thing that is meant to still be there a year later.
The carrier gel is resorbed over roughly the first two to three months. The microspheres stay.
Left behind in the tissue, the microspheres act as a scaffold. Fibroblasts move in around them and lay down new collagen and elastin. A 2026 review of the material in the tissue-engineering literature summarises it as providing "structural support" while stimulating "collagen synthesis by activating fibroblasts, leading to sustained improvements in skin quality, volume restoration, and contour enhancement." The same review names "the absence of reversal agents" as a known limitation of the material.
There is a laboratory study comparing how immune cells respond to calcium hydroxylapatite and to poly-L-lactic acid, the material in Sculptra. It reported that poly-L-lactic acid raised inflammatory signalling molecules in human macrophages while calcium hydroxylapatite did not, and concluded the two materials act by different routes. That study was run and authored by research staff at Merz Aesthetics, which makes Radiesse, and the comparator was a competitor's material. The finding is worth knowing and the sponsorship is worth knowing with it.
Nothing is left behind permanently: The microspheres are progressively degraded into calcium and phosphate ions and handled by ordinary mineral metabolism. The FDA labelling does not describe this process, so it comes from the review literature rather than the label.
The new collagen is not permanent either, and this is the part most explanations skip. Collagen made in response to a filler turns over like any other collagen in the skin. That is why the aesthetic effect fades over time even though collagen was genuinely made. "It stimulates your own collagen" and "the result lasts forever" are not the same statement, and only the first one is supported.
Hyperdilution means mixing Radiesse with extra saline, often with lidocaine, before injecting: More dilution means the product spreads more widely, lifts less, and behaves more like a skin treatment than a contouring one.
A dilution ladder is described in the continuing-education literature: undiluted for deep structural support, 1:1 and 1:2 for volume and transitions, and 1:3 or 1:4 to spread over wide areas such as the neck, décolleté, arms or abdomen. That ladder is case-series-level material published through a continuing-education activity by a faculty group with extensive Merz links. It is a convention, not a tested protocol.
On the regulatory side the position is simple: the only approved dilution is 1:2 with 0.9% saline, and only for the décolleté, approved in March 2026. Facial and body hyperdilution at 1:3 or 1:4 is off-label — which is legal and done routinely, but it means no regulator has reviewed evidence for it.
The published efficacy data are thin by design. The most cited example is a retrospective chart review of 22 patients given two sessions of 1:3 hyperdilute Radiesse to the mid and lower face; 3D imaging at day 150 showed a significant increase in cheek volume and reductions in jowl volume and in the depth of nasolabial folds and marionette lines. It had no control group and its authors classified it as Level 4 evidence. A separate review of hyperdilute technique was written by a Merz consultant.
Radiesse reached the market through the FDA's premarket approval route, which required clinical evidence for named indications. Those named indications are:
Facial wrinkles and folds, "such as nasolabial folds", and HIV-associated facial lipoatrophy: Both approved 22 December 2006, under PMA P050052 and P050037 respectively
Hand augmentation to correct volume loss in the dorsum of the hands: Approved 4 June 2015
Moderate to severe loss of jawline contour in adults over 21, for Radiesse (+) Lidocaine, by deep subdermal and/or supraperiosteal injection — approved 1 September 2021
Correction of décolleté wrinkles in patients 22 and older, using a 1:2 dilution with saline — approved 31 March 2026
Injecting Radiesse anywhere else is off-label, and off-label use is legal and routine across medicine. It is not a scandal and it is not a loophole. What it does mean is that for those areas there is no FDA-reviewed trial for this product, so the evidence has to be judged on its own.
One area is called out in the label itself. For the lips, the labelling states that safety and effectiveness has not been established, and adds that there have been published reports of nodules after Radiesse was injected into lips. A 2013 evidence review makes the same point in clinical terms, advising against calcium hydroxylapatite in highly mobile areas such as the lips and in unforgiving areas such as around the eyes, because of nodules.
Radiesse is radiopaque — it is visible on imaging: This is stated in the labelling and it is a real practical fact rather than a curiosity.
When the FDA approved the hand indication in 2015, one of the required post-approval studies was a radiological study in 20 patients specifically testing whether Radiesse obscures the bones of the hand on x-ray across repeat treatments over two years.
When an FDA advisory committee met in August 2025 to discuss fillers in the décolletage, one of the agency's stated concerns was interference with breast cancer screening — that filler could mask an underlying malignancy on mammography, and that filler nodules could be mistaken for suspicious breast masses or the reverse. The decollete indication was approved the following year.
The practical takeaway: tell radiologists, mammography technicians and dentists that you have had Radiesse, and where: An unexplained bright spot on a scan is a problem worth avoiding.
Go to an emergency department or call 911 if, during or after any filler injection, you have:
Sudden vision change, double vision or loss of vision in either eye
Sudden severe pain, or pain out of proportion to the procedure
Skin that turns white (blanching) and then dusky, mottled or net-like
Weakness, drooping, slurred speech or any other stroke-like symptom
These can be signs that filler has entered an artery. Time matters in hours. Published guidance treats suspected retinal artery occlusion as a same-hour emergency and suspected skin occlusion as a same-day emergency, though that window comes from a 1980 primate experiment and from expert consensus, not from trials in filler patients.
Do not wait to see whether it settles, and do not use pain as your gate. In a survey of 52 experienced injectors worldwide, pain was mild or absent in 47% of the intravascular injections they reported.
Radiesse raises the stakes here: Hyaluronic acid fillers can be broken down with hyaluronidase in an emergency. Calcium hydroxylapatite cannot, and there is no approved reversal agent for it, so the response is supportive care rather than dissolving the product.
Swelling keeps growing after the first few days instead of settling
A lump appears and does not settle
Redness spreads outward from the injection site
Tenderness, redness or a firm lump turns up weeks or months later — a delayed inflammatory reaction or an infection is possible
The product looks as though it has moved from where it was placed
None of these is an emergency in the same sense as the list above, but all of them are reasons to be seen rather than to wait it out.