What is a collagen-stimulating filler and how does it work?
Collagen is the supporting protein that gives the skin firmness and fullness, and it decreases with age. In medical language, collagen-stimulating fillers are also called biostimulants or biostimulators. In these products, very small particles are injected under the skin in a carrier gel or liquid. The carrier is absorbed within a short time; the particles left behind set off a controlled tissue reaction around them, and the body produces new collagen around these particles. In other words, a significant part of the fullness you see comes not from the product itself but from the response of your own tissue.
This response varies from person to person and cannot be fully predicted in advance; this is why the method progresses slowly and its result is not as predictable as that of hyaluronic acid fillers.
| Substance | What it is | Distinguishing feature |
|---|---|---|
| Poly-L-lactic acid | A man-made polymer that is broken down in the body and is also used in dissolvable surgical stitches | Does not give immediate volume; it is given as a series of injections spread over months, and the effect becomes gradually more noticeable over weeks |
| Calcium hydroxylapatite | Particles of a mineral found naturally in teeth and bone, suspended in a gel | Also gives some volume when injected; visible on X-rays and CT scans |
| Polycaprolactone | Microspheres of a polymer that is broken down in the body, suspended in a gel | Both volume and collagen stimulation are aimed for; in the USA it is not listed among the FDA's approved filler materials |
How does it differ from hyaluronic acid filler?
| Feature | Hyaluronic acid filler | Collagen-stimulating filler |
|---|---|---|
| When is the effect seen | Immediately after the procedure | Gradually, over weeks and months |
| Where does the effect come from | From the volume the gel occupies | Largely from new collagen produced by the tissue |
| How long does it last | Measured in months | Often longer than a year; varies with the person and the product |
| Can it be reversed | Can largely be dissolved with the enzyme hyaluronidase | Cannot be dissolved with an enzyme; you have to wait for the body to break it down |
The 'can it be reversed' row of the table is the difference that deserves the most thought when deciding. Hyaluronidase breaks down only hyaluronic acid; it has no effect on these products. The FDA also states that removing fillers not made of hyaluronic acid may be difficult and sometimes impossible. For a result you do not like, an asymmetry or a palpable firm area, there is no option of 'let's dissolve it'. What dissolving filler involves is covered in the article “Dissolving Filler (Hyaluronidase)”, and a general account of hyaluronic acid fillers in the article “Hyaluronic Acid Filler”.
These products are also known popularly by different names. They do not belong to the same group as fillers that are never broken down in the body (such as liquid silicone); they are broken down over time. Even so, because they stay in the tissue for a long time and cannot be dissolved with an enzyme, their possible late problems are dealt with together in the article “Complications of Permanent and Semi-Permanent Fillers”.
What are they used for, and what are the approved uses?
The US Food and Drug Administration (FDA) states that fillers absorbed by the body are approved in adults aged 22 and over for moderate to severe facial wrinkles and folds, and also for adding volume to the lips, cheeks, chin and back of the hands. Correcting facial fat loss in people living with HIV is also among the approved uses. Each product has been approved for only some of these uses. In the FDA's list of materials, calcium hydroxylapatite is described for facial wrinkles and the back of the hands, and poly-L-lactic acid as a long-lasting filler given in sessions spread over months.
In recent years it has become common for calcium hydroxylapatite to be diluted and injected in order to tighten the skin in areas such as the neck, décolletage, arms, abdomen or buttocks. The international consensus paper published for this use states plainly that it is a new use falling outside the approved indication and that the recommendations are preliminary. The FDA also warns against using fillers for body contouring purposes such as breast and buttock enlargement, and reports that injections between the eyebrows, in the nose, around the eyes, in the forehead and in the neck are not among the approved uses either.
Which product is registered for which purpose in Turkey is a separate matter. Ask your physician for the name and content of the product recommended to you, and whether the recommended area is included in the product's instructions for use.
Who may they be suitable for?
- Adults with widespread loss of facial volume that has developed with age or weight loss, who are prepared to wait months for the result
- People who want to soften hollowing over broad areas such as the cheeks and temples, rather than a single line
- People who decide in the knowledge that the result cannot be reversed, that more than one session may be needed and that the response varies from person to person
Whether the change in the face is due to volume loss or to skin laxity determines the result; in marked sagging the effect to be expected from these products is limited.
Who are they not suitable for, and what should you watch out for?
- Pregnancy and breastfeeding: safety data are insufficient; the procedure is generally postponed.
- Active infection, inflamed spots, a cold sore or an open wound in or near the treatment area
- A history of allergic reaction to one of the product's components or to local anaesthetic
- A tendency to form raised scars (keloids)
- Conditions or medicines that affect the immune system: the response of the tissue may be unpredictable; the decision rests with the physician.
- A bleeding disorder or use of blood-thinning medicines: do not stop your medicine on your own; talk to your physician.
- An old filler in the same area whose content is unknown or which does not break down in the body
- Thin-skinned, very mobile areas such as the lips and around the eyes: nodules form more easily and are more conspicuous in these areas; treatment with these products is generally avoided there.
This list is not complete. Describe in full all your medical conditions, the medicines and supplements you take, and the fillers and other aesthetic procedures you have had before.
Who should perform it, and where?
As with all fillers, the most serious risk with these products is the substance being accidentally injected into a blood vessel and blocking it. The FDA reports that this can lead to tissue death, loss of vision and stroke. With hyaluronic acid filler the physician has an enzyme that can be used against vascular occlusion; with collagen-stimulating fillers there is no such dissolving agent. For this reason the treatment needs to be performed in a healthcare facility by a physician who knows facial anatomy well and can recognise and manage a complication.
How the product is diluted and prepared, and the depth at which it is placed, directly affect the result and the risk of nodules; these details are specific to the product. The general framework on who is authorised is explained in the article “Who Can Perform Medical Aesthetic Treatments?”. Ask for the product box to be opened in front of you and for the product name and batch number to be given to you in writing.
Preparing for the procedure
- During the examination, volume loss, skin thickness and facial proportions are assessed; the aim, the number of sessions and the expected duration are discussed.
- Mention all the fillers you have had before, even if you do not know the product name.
- Ask your physician about medicines and supplements that may increase bruising; do not stop your prescription medicines yourself.
- Report any dental treatment or vaccination planned in the near future, or any illness with fever; your physician will assess the timing.
- Because the result comes slowly, do not try to fit the procedure in before an important event; also allow time for the swelling and bruising of the first days.
- Read the consent form without hurrying; make sure it has been clearly explained to you that the product cannot be dissolved.
With collagen-stimulating fillers the result appears over weeks and months, through the tissue's own response, and these products cannot be dissolved with an enzyme as hyaluronic acid fillers can. That is why the decision should not be rushed; ask for a written record of which product was used, and show any firmness you notice later to your doctor without trying to disperse it by massage.
Dr. Hamza GemiciMedical Director, DoktorClub · Aesthetic Medicine Physician
The day of the procedure, step by step
- The physician assesses your face at rest and with facial expressions, and marks the areas to be treated. Photographs are usually taken for the record.
- The informed consent form is read, the risks and options are discussed, and the form is signed.
- The skin is cleaned with an antiseptic solution.
- A numbing cream may be applied to reduce discomfort; some products are prepared by mixing them with local anaesthetic.
- The product is placed in small amounts under the skin or deeper, with a fine needle or a blunt-tipped cannula. The physician decides which instrument to use; no instrument eliminates the risk of vascular occlusion.
- Throughout the treatment the physician watches the colour of the skin and how you respond. If you feel sudden, severe or unusual pain, a change in vision or dizziness, say so immediately.
- At the end of the procedure the physician may massage the area. Before you leave, the skin colour is checked; aftercare advice and details of how to reach the physician are given.
Even with numbing, the procedure is not free of pain; most people describe prickling, pressure and a feeling of fullness.
After the procedure: the first 24 hours, the first week, the first month
- First 24 hours: there may be swelling, redness, tenderness and bruising at the needle sites. Check the skin colour several times. Stay away from intense exercise, saunas, Turkish baths and very hot environments.
- First week: swelling and bruising gradually decrease. As the carrier liquid or gel is absorbed, the fullness of the first day may lessen; this does not mean the product has not worked.
- Massage: do it only if your physician has recommended it, and in the way recommended. If it has not been recommended, do not press on or rub the area.
- First month: new collagen forms slowly; a marked change may not yet be visible. If you notice a palpable firm area, a lump or new swelling, tell your physician without waiting for the next session.
Is massage necessary? Why do the instructions differ?
For years after poly-L-lactic acid treatments, patients were advised to massage regularly, several times a day for days, in order to reduce nodule formation. How necessary this advice is remains a matter of debate. In a randomised study of 20 people using current dilution and injection technique, no nodules were seen at six months of follow-up in either the group that massaged or the group that did not, and the result was not found to differ either. The study is small and is not sufficient on its own to reach a firm conclusion.
For this reason practice differs between physicians, and massage instructions also vary with the product. Act on the instructions given to you by the physician who performed the procedure, not on a rule you have read on the internet. And do not try to disperse a firm area that appears weeks later by massaging it; an examination is needed first.
Expected side effects, and the risk of nodules and granulomas
- Swelling, redness and tenderness: mostly decrease within days.
- Bruising: common at the needle sites.
- A temporary feeling of fullness and tightness
- In the first weeks, small firm areas that can be felt on touch but are not visible from outside
The most important problem specific to this group of products is the nodule. A nodule is a hard lump under the skin that can be felt and is sometimes visible from outside. The scientific literature distinguishes two separate situations: nodules that appear in the first weeks are mostly due to the product collecting at one point or being placed too superficially. A granuloma, by contrast, is an excessive inflammatory response of the body to the particles; it usually appears after a silent period lasting months, and often at all the treated points at the same time.
The consensus paper on diluted calcium hydroxylapatite states that placing lightly diluted product too superficially in thin and dark-coloured skin can lead to more problems. For polycaprolactone, in a study looking back at 1,111 treatments by a single physician, no nodules or granulomas were reported, and swelling lasting longer than two weeks was seen in about one in twenty treatments. This study was conducted at a single centre and part of the data is based on telephone interviews; it is not sufficient to show how great the risk really is. The same study emphasises that this product cannot be removed with an enzyme either.
Treating nodules and granulomas is difficult because the product cannot be dissolved; depending on the situation, the physician considers monitoring, injecting medication into the area or other methods. The details are explained in the article “Complications of Permanent and Semi-Permanent Fillers”, and the problems that can be seen with all fillers in the article “Filler Complications”.
Contact the physician who performed the treatment immediately (if you cannot reach them, go to the nearest emergency department)
- Blanching, marked paleness or a purplish discolouration spreading like a net in or around the treatment area
- Sudden, severe or steadily increasing pain
- Swelling, redness, increased warmth, discharge or fever that increases as the days go by
- A firm area that grows quickly, is painful or turns red
Call 112 (or your local emergency number) without delay or go to the nearest emergency department
- Blurred vision, loss of vision, double vision or severe pain in the eye
- Impaired speech, drooping of the face, weakness in an arm or leg
- Shortness of breath; rapidly increasing swelling of the lips, tongue or throat
What to do if these symptoms occur is explained step by step in the article “After Fillers: When Is It an Emergency?”. In the emergency department, say which product was used and that it is not hyaluronic acid.
Why should you mention it when having an X-ray, a dental X-ray or a CT scan?
The FDA states that calcium hydroxylapatite will be visible on X-rays for as long as it remains in the body and may obscure the structures beneath it. Dental and radiology publications have reported that this filler appears as dense, bright areas on jaw X-rays and on computed tomography. In a case series of five patients it was stated that the same filler also showed uptake on PET scans used in cancer follow-up and could lead to a false-positive finding.
This does not mean the filler is harmful; however, the physician interpreting the image needs to know about it. When you have a dental or jaw X-ray, a CT scan, an MRI or a PET scan, tell your dentist and the radiology team which filler was placed in your face or hand, and when. This is why it is important to keep the product name and the date of the procedure. The sources for this article do not contain sufficient information on how poly-L-lactic acid and polycaprolactone appear on imaging; even so, it is right to report every filler.
How many sessions are needed, when is the result seen, and how long does it last?
The number of sessions varies with the substance, the area and the degree of volume loss. The FDA states that poly-L-lactic acid is given as a series of injections spread over several months, that its effect becomes gradually more noticeable over weeks and that it may last up to two years. For calcium hydroxylapatite the FDA gives a duration of effect of about 18 months. These durations are average figures; how long it will last for you cannot be stated in advance.
Because the result comes slowly, patience is needed. In the weeks after the first session, the feeling that 'nothing has changed' is common. Hurrying to have more product added during this period can lead to an excess that cannot be reversed once the collagen response appears; the decision on further treatment should be made by examination.
Realistic expectations: what can they not do?
- They do not tighten marked sagging; they do not replace a surgical lift.
- They do not correct fine superficial lines, dark spots or pores.
- The fullness seen on the day of the procedure is not the final result; the result emerges over months.
- How much collagen will form cannot be known in advance; a difference may remain between the two sides.
- No promise can be made about the result, and if you do not like it, it cannot be reversed by dissolving.
- They do not stop ageing; the effect lessens over time.
Alternatives
| Method | What it does | Point to note |
|---|---|---|
| Having no procedure at all | The option of waiting without taking any risk | Always a valid option |
| Hyaluronic acid filler | Volume that is seen immediately; correcting a specific point | Its effect is shorter; it can be dissolved with an enzyme when necessary |
| Skin booster injections | Hydration and skin quality, not volume | Evidence is limited for many products |
| Energy-based tightening (HIFU, radiofrequency) | Moderate tightening in mild laxity | Does not add volume; the effect is limited |
| Surgical facelift | The strongest effect in marked sagging | It is an operation; it has a recovery period and surgical risks |
Volume treatments for the cheeks and jawline are covered in the article “Chin and Cheek Filler”, and injections aimed at skin quality in the article “Skin Booster Injections”.
This content is for information purposes; it does not replace an examination. The method that suits you can only be determined by a physician's assessment.
Aftercare timeline
Treatment day
There may be swelling, redness, tenderness and bruising at the needle sites. Check the skin colour several times: if there is blanching, a purplish discolouration spreading like a net or severe pain, call your physician immediately; for problems with vision or speech, call 112 (or your local emergency number). Stay away from intense exercise, saunas and Turkish baths.
Day 1
Massage only if your physician has recommended it, and in the way recommended; if it has not been recommended, do not press on or rub the area. Continue to avoid very hot environments.
Day 3
Swelling and bruising begin to decrease. If you have swelling, redness, increased warmth, discharge or fever that increases as the days go by, contact your physician.
Day 7
As the carrier liquid or gel is absorbed, the fullness of the first day may lessen; this is expected and does not mean the product has not worked.
Day 14
A marked change may not yet be visible; new collagen forms slowly. If you notice a palpable firm area or lump, do not try to disperse it by massage; tell your physician.
Day 30
If more than one session is planned, the next session may be approaching; the decision on further treatment is made by examination. Keep the product name and the date of the procedure; mention the filler when you have a dental X-ray or CT scan.
Questions to ask your physician
- What is the active substance of the product you are recommending to me; can I have the product name and batch number in writing?
- Is this product being used in the recommended area in line with its instructions for use, or is this an off-label use?
- Why do you recommend this rather than hyaluronic acid filler in my case?
- How many sessions do you anticipate, and when will we assess the result?
- What can be done if I do not like the result or a nodule develops?
- Should I massage after the procedure; if so, how and for how long?
- How do you intervene with this product in an emergency such as vascular occlusion?
- Do I need to mention this filler when I have a dental X-ray or CT scan?
Frequently asked questions
Can a collagen-stimulating filler be dissolved?
No. The enzyme hyaluronidase used to dissolve filler breaks down only hyaluronic acid; it has no effect on poly-L-lactic acid, calcium hydroxylapatite or polycaprolactone. These products are broken down by the body over time, but this process cannot be speeded up.
When is the effect of a collagen-stimulating filler seen?
The effect appears not immediately but gradually, over weeks and months, because the result depends on the new collagen produced by the tissue. Part of the fullness seen on the day of the procedure is due to the carrier liquid and may lessen within days.
How long does a collagen-stimulating filler stay?
The FDA states a duration of effect of up to two years for poly-L-lactic acid and about 18 months for calcium hydroxylapatite. These are average figures; the duration varies with the person, the product, the amount and the area, and cannot be stated precisely in advance.
Is massage essential after the procedure?
This is a matter of debate and varies with the product. For poly-L-lactic acid, regular massage was recommended for many years, while a small study found no difference between the groups that did and did not massage. Follow only the instructions given by the physician who performed the procedure.
I can feel a firm area weeks later; is this normal?
In the first weeks there may be small firm areas that can be felt on touch; however, firm areas that grow, become visible, are painful or appear months later may be nodules or granulomas. Show them to your physician without trying to disperse them by massage.
Are these fillers visible on dental X-rays or CT scans?
Calcium hydroxylapatite is visible on X-rays and CT scans; it may obscure the structures beneath it and, if not known about, may be mistaken for another condition. When having imaging, tell your dentist and the radiology team which filler was placed and when.
Sources
- Dermal Fillers (Soft Tissue Fillers) — U.S. Food and Drug Administration (FDA), 2023
- FDA-Approved Dermal Fillers — U.S. Food and Drug Administration (FDA), 2020
- The Efficacy of Massage in Reducing Nodule Formation After Poly-L-Lactic Acid Administration for Facial Volume Loss: A Randomized, Evaluator-Blinded Clinical Trial (Wu DC, Goldman MP). Dermatol Surg 42(11):1266–1272. PMID: 27618389 — Dermatologic Surgery, 2016
- Global Consensus Guidelines for the Injection of Diluted and Hyperdiluted Calcium Hydroxylapatite for Skin Tightening (Goldie K et al.). Dermatol Surg 44 Suppl 1:S32–S41. PMID: 30358631 — Dermatologic Surgery, 2018
- Polycaprolactone-based dermal filler complications: A retrospective study of 1111 treatments (Lin SL, Christen MO). J Cosmet Dermatol 19(8):1907–1914. PMID: 32485052 — Journal of Cosmetic Dermatology, 2020
- Foreign body granulomas after all injectable dermal fillers: part 2. Treatment options (Lemperle G, Gauthier-Hazan N). Plast Reconstr Surg 123(6):1864–1873. PMID: 19483588 — Plastic and Reconstructive Surgery, 2009
- Radiological impact of the use of calcium hydroxylapatite dermal fillers (Feeney JN, Fox JJ, Akhurst T). Clin Radiol 64(9):897–902. PMID: 19664480 — Clinical Radiology, 2009
Medical Aesthetics Expert Board
This article has been reviewed by the DoktorClub Medical Aesthetics Expert Board.
