Two materials do this work. Poly-L-lactic acid, sold as Sculptra, is a particle the body responds to by building collagen around it, and it adds essentially no volume of its own. Calcium hydroxylapatite, sold as Radiesse, does both: its gel carrier occupies space immediately, and the microspheres suspended in it stimulate collagen afterward. Everything below is in vials and syringes, because that is the unit these are bought and quoted in.
What happens, and when
The figures in this section come from biopsy studies that stained treated tissue at intervals and counted what was there. They describe a biological response rather than a guaranteed appearance, and the two are related but not the same thing.
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Day 0
You leave fuller than you arrived, and that is not the result
A vial of poly-L-lactic acid is reconstituted in anywhere from 8 to 17 mL of fluid before it is injected, and on the body that figure sits at the top of the range. Most of what goes in is water. It produces real fullness on the day, and people read that fullness as the treatment working.
It is not. Calcium hydroxylapatite behaves differently, because its carrier gel does occupy space from the moment it is placed, so some of what you see at the end of a session there is genuinely volume. With poly-L-lactic acid, almost none of it is.
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Days 2 to 3
Back to where you started
The diluent resolves and the face or the body returns to close to its starting point. This is the part almost nobody is warned about, and it is where people decide the treatment failed.
It did not fail. Nothing has happened yet, because nothing is supposed to have happened yet.
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The first five days
Massage, and why it is not optional
Starting the day of the session and running for five days: five minutes, five times a day, after a poly-L-lactic acid treatment. It distributes the particles through the tissue rather than letting them sit as a concentration, and that is what keeps nodules from forming. On the neck and chest the technique changes: firm massage with liquid soap immediately after the session, done in the room before you leave.
Skipping it is the most common reason a result comes out uneven, and it is the one part of this that is entirely in your hands.
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Day 30
New blood supply, none of it visible
The first measurable change is vascular rather than structural. New vessels are visible on staining thirty days after treatment, and the marker for them rises by roughly half over the following months. Blood supply comes before the building, which makes sense and is still invisible from the outside.
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Month 4
Type III collagen peaks
Collagen comes in two relevant types and they do not arrive together. Type III is the provisional kind, laid down fast and loosely organized, and it peaks here at around 75 percent above where it started. Type I, the mature structural kind, has risen only about 14 percent at this point.
This is when most people first notice something, and what they are noticing is scaffolding rather than the finished structure.
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Month 6 to 7
The swap, and the month the result is read
Type I collagen reaches roughly a third above baseline. Type III falls back toward normal. The provisional scaffold has been replaced by the mature one, which is the actual point of the treatment.
Elastin rises alongside it, in one study by around 73 percent at seven months. Elastin is what lets skin recoil rather than merely sit there, and it is the thing almost nothing else in aesthetics meaningfully adds. This is why a biostimulator result is judged at six months and not before, and why judging it at six weeks tells you nothing.
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Month 12
Still rising
Collagen I and III remain elevated and elastin continues to climb through the twelfth month, which is the last point most studies measure. The result at a year is generally better than the result at six months, which is the opposite of how filler behaves.
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Months 12 to 15
The product is gone
The calcium hydroxylapatite microspheres have been metabolized and cleared by this point. Poly-L-lactic acid breaks down on a similar scale. Nothing injected remains in the tissue.
What remains is collagen and elastin your own body made, which is the whole premise and also the reason none of this can be dissolved. Hyaluronic acid filler can be reversed with an enzyme. A biostimulator result cannot be, because by the time you would want to reverse it there is nothing left to dissolve.
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Months 18 to 30
What is left is yours
Poly-L-lactic acid results are described as lasting up to two years after a full series. Structural improvement after calcium hydroxylapatite has been reported out to 30 months. Both then fade the way your own collagen fades, gradually, rather than deflating.
What each area takes
Amount here is driven by surface area more than by severity, which is why a body area takes several times what a face does. The ranges below come from the published consensus protocols and the product labeling. They describe what is standard, not a plan for any particular person.
Select an area to highlight it. Every area is listed in full alongside.Tap an area for what it treats and what it takes. Every area is listed below.
Face
Poly-L-lactic acid1 to 2 vials per session, 3 sessions
Temples, cheeks and the midface, where volume loss starts. Sessions run 4 to 6 weeks apart and the result is read at six months. This is the longest studied use of the material, and the one with the most published data behind it. Lasts up to two years after a full series.
Neck
Either material1 to 2 vials or syringes per session, 2 to 4 sessions
Crepiness and loss of firmness rather than the vertical bands, which are a muscle problem and treated with a neuromodulator instead. Poly-L-lactic acid is reconstituted at 8 to 17 mL here and sessions sit at least four weeks apart; diluted calcium hydroxylapatite is an alternative at roughly 1 part product to 2 to 4 parts saline. Which one suits you depends on how much laxity there is and how thin the skin is, and that is an examination question rather than a preference.
Decolletage
Calcium hydroxylapatite, diluted1 to 2 syringes per session, 2 to 3 sessions
The crosshatched creasing across the chest, which is mostly sun rather than age and shows up earlier than people expect. This is among the better studied areas here, with its own clinical trial behind it rather than extrapolation from the face.
Hands
Either material1 to 1.5 mL per hand, or half to 1 vial per hand
Thin skin with tendons and veins standing out. Calcium hydroxylapatite has been studied specifically for the back of the hand and gives an immediate improvement on top of the collagen built afterward. Up to 3 mL per hand has been used, though more than about 1.6 mL in a repeat session has been associated with more side effects, so the practical amount sits below that.
Upper arms
Poly-L-lactic acid1 vial per side per session, 2 to 4 sessions
Laxity on the inner and back of the upper arm, which responds to skin quality work rather than to volume. Up to 1.5 vials a side where laxity is more marked. Sessions a minimum of 30 days apart. Improvement in texture has been reported after the first session and described as still present at 22 months.
Abdomen
Poly-L-lactic acid1 to 3 vials per session, up to 3 sessions
Crepe-textured, loose skin, most often after weight loss or pregnancy. Treated above the navel as well as below it. Sessions about 45 days apart, and the published series describe marked improvement at the twelve-month assessment rather than at three.
Buttocks
Poly-L-lactic acidUp to 3 vials per side per session, up to 3 sessions
Dimpling, crepiness and modest recontouring, placed roughly 70 percent in the upper region and 30 percent in the lower. Shallower placement addresses dimpling and deeper placement in the upper quadrant does the lifting. Sessions 4 to 6 weeks apart. This is not the same thing as a large-volume augmentation, which is a separate procedure with a different risk profile and is not performed here.
Thighs
Poly-L-lactic acidUp to 2 vials per area, 3 sessions
Dimpling and texture on the outer and inner thigh, injected in a fan just under the skin. Three sessions four weeks apart. The published figures describe roughly a 40 percent reduction in the depth of depressions and about a 22 percent improvement in appearance, which is a real change and not a transformation.
Knees
Poly-L-lactic acid1 vial per knee, 3 sessions
The loose, crinkled skin above the kneecap, which almost nothing else treats and which people are often surprised can be treated at all. Three sessions four weeks apart, with improvement measured at roughly three months and still present at six.
How well studied each area is
These areas are not all equally well studied, and it is worth knowing which is which before you decide. The face, the back of the hands and the decolletage have the strongest evidence behind them, each with its own trials. The rest of the body rests on a different kind of study.
That study is real and it is reassuring. A 2024 international consensus published per-area protocols for the body, and a 2026 review of 1,651 body sessions across nine United States clinics reported nodules in one patient out of 498 and no granulomas. That is a large number of treatments with a very low complication rate, which is the most useful thing anyone can tell you about safety. What it is not is randomized, and the panel that wrote the consensus said so in its own assessment.
One distinction matters more than the rest. Large-volume body contouring, where liters of material are placed to change the shape of a body part, is not safe and is not done here. It has caused serious injury and death, and no amount of technique makes that an acceptable trade. Treating the buttock at up to three vials a side for dimpling and skin quality is a different procedure entirely, and conflating the two helps nobody.
What a vial count does not tell you
How much the product was diluted, how deep it was placed, and whether the massage was actually done. All three change the result more than the number does, and the first two are where most of the difference between a good biostimulator outcome and a disappointing one lives. Deeper placement and a generous reconstitution volume are what keep nodules from forming; shallow placement in too little fluid is what causes them.
So ask for the count, and ask what it was mixed into and what plane it is going into. A quote that gives you a number alone is describing the purchase, not the treatment.
Common questions
Why do I look the same two weeks later?
Because nothing has happened yet. The fullness on the day came from the fluid the product is mixed into, not from the product, and it resolves in two or three days. The first measurable biological change is new blood supply at around thirty days, and the first collagen worth noticing arrives at about four months. A biostimulator is the one treatment in aesthetics where looking unchanged early is the expected course rather than a bad sign.
Is hyperdilute better? It is marketed as the advanced version.
Not in the way the name suggests. More dilution spreads the product over a wider area, which is why it is used on large surfaces like the abdomen or the back of the arm. But the laboratory work points the other way on potency: collagen production was highest at a 1 to 1 dilution, where there is enough space between particles for cells to migrate but the particles are still close enough together to signal. It remained elevated out to roughly 1 to 6.5, so hyperdilution still works. It is a coverage decision rather than a strength upgrade, and anyone selling it as the stronger option has it backward.
Can it be dissolved if I do not like it?
No, and this is the real trade against filler. Hyaluronic acid can be reversed with an enzyme within a day or two. Neither of these materials can be, because the result is not the material. It is collagen your body built, and there is nothing to dissolve. That makes placement and patient selection matter more here, and it is the main reason a conservative first session is worth more than an ambitious one.
What about nodules?
They are the characteristic complication and they are uncommon when the technique and the aftercare are right. The largest recent look at body treatment, a multicenter review of 498 patients across 1,651 sessions in nine United States clinics, found nodules in a single patient, 0.2 percent, and no granulomas at all. The overall adverse event rate was 6.6 percent and was mostly bruising. The things that reduce the risk are injecting deep rather than shallow, using a generous reconstitution volume, and doing the massage, which is why the massage is not presented here as a suggestion.
Is this safe in darker skin?
Skin tone does not change how either material works. There is no light and no heat involved, so there is no chromophore and no question of pigment absorbing energy. What does matter is that a needle puncture in deeper skin can leave a dark mark while it heals, so technique shifts toward fewer entry points and a cannula where the area allows one. A history of keloid or hypertrophic scarring is a specific contraindication for poly-L-lactic acid and is worth raising before anything is planned.
How many vials will I actually need?
On the face, usually two to four across a full series. On the body it is a different order of magnitude: the published average is four vials in a single session, and across a full course of treatment the average patient in that series received thirteen. The number is driven by surface area more than by severity, which is why a body area costs what it does and why quoting it per vial rather than per area is the only honest way to do it.
Can I have this and filler at the same time?
At different visits, usually. They answer different questions. Filler replaces volume where volume was lost and does it today; a biostimulator improves the quality and thickness of the tissue itself over months. A face that needs structural volume restored and also has thin, crepey skin often wants both, sequenced rather than stacked, so that what each one did can be told apart.
What does a biostimulator not do?
It does not lift loose skin. It thickens and firms the tissue, which reads as tighter, but skin that has genuinely gone lax needs either an energy device or surgery, and more vials will not substitute for either. It also does not work on anyone's schedule but its own. If you need to look different in three weeks, this is the wrong treatment, and no amount of product changes that.
Back to biostimulators → · Biostimulators or filler · What actually stimulates collagen
References
- Aguilera SB, McCarthy A, Khalifian S, Lorenc ZP, Goldie K, Chernoff WG. The role of calcium hydroxylapatite (Radiesse) as a regenerative aesthetic treatment: a narrative review. Aesthetic Surgery Journal. 2023;43(10):1063-1090. PMC11025388
- Haddad A, Avelar L, Fabi SG, et al. Injectable poly-L-lactic acid for body aesthetic treatments: an international consensus on evidence assessment and practical recommendations. Aesthetic Plastic Surgery. 2025;49(5):1507-1517. doi.org/10.1007/s00266-024-04499-9
- Durairaj KK, et al. Nonfacial use of injectable poly-L-lactic acid: safety data from a multicenter observational study in the United States. Aesthetic Surgery Journal Open Forum. 2026;8:ojag053. doi.org/10.1093/asjof/ojag053
- Sculptra Aesthetic instructions for use. Galderma Laboratories. galderma.com
- Radiesse injectable implant instructions for use for the dorsum of the hand. FDA PMA P050052/S049. accessdata.fda.gov
- Merz Aesthetics receives FDA approval for Radiesse for the treatment of wrinkles in the decollete area. April 2026. merzaesthetics.com
- Dermal filler do’s and don’ts for wrinkles, lips and more. U.S. Food and Drug Administration consumer update. fda.gov
This article is for general education and is not medical advice. It does not establish a physician-patient relationship, and it cannot account for your individual history or skin. Treatment decisions should be made in consultation with a qualified clinician who has examined you. Product names are referenced for clinical accuracy; Aahana Medical Aesthetics has no financial relationship with the manufacturers named.