What is the Difference Between HA and Non-HA Fillers, and Can They Really All Be Dissolved?
Author: In-Yong Kim, MD | Lieul Dermatology Clinic, Director | Specialty: Dermatology
Published: September 1, 2026
Last updated: September 1, 2026
This article provides general medical information on the composition, longevity, and adverse effects of cosmetic dermal fillers, based on guidance from the Korean Ministry of Food and Drug Safety and original research articles from Korea and abroad. It is not a substitute for individualized diagnosis or treatment, and responses and outcomes vary between individuals.
What Are Dermal Fillers Made Of?
A filler is not the name of a single substance. It is a collective term for several materials used to physically fill soft tissue.
The most widely used is hyaluronic acid (HA). Others include calcium hydroxylapatite (CaHA), poly-L-lactic acid (PLLA), and polycaprolactone (PCL).
The Korean Ministry of Food and Drug Safety (MFDS) defines a cosmetic dermal filler as a medical device injected subcutaneously to fill facial wrinkles for visual improvement, maintaining its own volume without pharmacological action.¹
That definition contains the key point. A filler is not a drug that alters physiology; it is a material that occupies a depleted space. What you fill with therefore largely determines both the result and the risk.
Is a Filler a Drug or a Medical Device?
In Korea, cosmetic dermal fillers are classified as medical devices rather than pharmaceuticals, and each product has a defined approved intended use.
The MFDS lists approved intended uses such as correction of facial wrinkles and volume restoration of the face and dorsum of the hand, and product-specific approvals can be searched directly through the medical device e-application portal.² In other words, an official route exists for patients to verify the approved scope of the product they are receiving.
What Is the Difference Between HA and Non-HA Fillers?
The decisive difference is reversibility. HA fillers can be removed with the enzyme hyaluronidase; non-HA fillers have no corresponding enzyme.
Type | Main component | Mode of action | Enzymatic removal | If a problem occurs |
|---|---|---|---|---|
HA filler | Cross-linked hyaluronic acid | Immediate volume filling | Possible (hyaluronidase) | Dissolved by enzyme injection |
CaHA | Calcium hydroxylapatite | Filling + collagen stimulation | Not possible | Corticosteroid / observation |
PLLA | Poly-L-lactic acid | Collagen stimulation | Not possible | Corticosteroid / observation |
PCL | Polycaprolactone | Filling + collagen stimulation | Not possible | Corticosteroid / observation |
Permanent | PMMA, silicone, etc. | Permanent retention | Not possible | Surgical removal required |
This difference matters less for aesthetic satisfaction than for emergencies: whether an antidote can be administered immediately if a vessel is occluded.
This does not mean non-HA fillers are inferior. Collagen-stimulating products produce gradual results that last longer. However, for a first treatment or in areas with complex vascular anatomy, considering a reversible option first is the more prudent approach.
How Effective Are Fillers in Practice?
Wrinkle correction and patient satisfaction have been demonstrated repeatedly in controlled clinical trials.
In randomized, double-blind studies of nasolabial folds, improvement on the Wrinkle Severity Rating Scale (WSRS) and responder rates were maintained non-inferiorly to comparator products, and aesthetic improvement and subject satisfaction remained durably high over 15 months.¹⁰
Specific longevity figures are also available. In a 24-month prospective randomized controlled trial of PCL fillers in nasolabial folds, sustained improvement was seen in 90% and 91.4% of patients at 12 months, and patient satisfaction at 24 months was 72.4% and 81.7% respectively.¹¹
Procedural discomfort is also lower than many expect. In one nasolabial fold study, mean pain during injection was 1.96 out of 10, adverse events were mild and transient, and median satisfaction scores were 9 to 10 out of 10 at each follow-up visit.¹²
Fillers are therefore not a poorly evidenced procedure. Used for the right indication, in the right plane, at the right volume, they produce reproducible results. What follows concerns the conditions for using this tool safely over time.
Do Fillers Really Dissolve Completely Within Six Months?
No. Imaging studies have repeatedly demonstrated residual filler for years.
In an MRI study of 33 patients who received HA filler in the mid-face, filler was detected in all 33. It remained in patients who had not been treated for two years, and detection up to 15 years was reported.³
In another 3D MRI study, the filler volume measured on MRI was on average 2.8 times the volume originally injected, and filler was still detectable at 180 months.⁴
Common counselling statement | Imaging findings |
|---|---|
Lasts 6–12 months | Present in all patients at 2 years; detected up to 15 years³ |
Retains the injected volume | Measured volume averaged 2.8× the injected amount⁴ |
It should be noted that residual filler is usually clinically silent. Persistence alone does not mean there is a problem.
The clinical implication concerns dosing. The assumption that everything has dissolved, so the same volume can be repeated, does not hold. Repeated layering in the same site may mean that later enzymatic treatment does not degrade the material evenly. This is why the timing and location of previous treatments should be confirmed before retreatment, with ultrasound used to check for residual material when needed.
What Adverse Effects Can Fillers Cause?
Most reactions are mild and resolve within days; serious complications are rare.
According to a systematic review, filler complications are reported at rates ranging from roughly 1 in 100 to 1–4 in 10,000 depending on the material used.¹³ Among 8,795 complications identified in the same review, serious adverse events comprised one case of mild skin necrosis and one abscess, while mild reactions such as pain, hematoma, edema, erythema, and nodules accounted for about 79.8% of the total.¹³ A systematic review of permanent complications likewise concluded that their incidence is low.¹⁴
The adverse effects listed by the MFDS include bruising, erythema, swelling, pain, softening, itching, rash, and redness.¹
Category | Symptoms | Onset |
|---|---|---|
Common reactions | Bruising, erythema, swelling, pain, itching¹ | Immediately after treatment to several days |
Delayed inflammatory reactions | Swelling, nodules, induration | From 2 weeks; mean 16.2 months⁵ |
Vascular complications | Skin necrosis, visual impairment, blindness, cerebral infarction⁶ | During treatment to within hours |
Can Fillers Cause Blindness?
It is extremely rare, but it has been reported. It occurs when filler enters a blood vessel or compresses one, causing occlusion.
On frequency, the US FDA states that the chance of unintentional intravascular injection is low, while noting that if it does occur the resulting complications can be serious and permanent, including vision abnormalities and blindness.¹⁵ In other words, this is treated as important because of the magnitude of the outcome, not its probability.
Vascular occlusion is reported as a severe adverse event that can lead to skin necrosis, visual impairment, permanent blindness, and rarely iatrogenic cerebral infarction.⁶ However, for occlusion caused by HA filler, immediate hyaluronidase-based treatment has been reported to improve prognosis.⁶
Reversibility is decisive here. This is why it is meaningful to confirm whether the clinic keeps hyaluronidase on hand and has a defined protocol for vascular complications.
A Lump Appeared Months After Treatment. Could It Be the Filler?
Yes. Delayed inflammatory reactions can appear from two weeks after treatment up to several years later.
In a study analyzing delayed complication cases, the mean interval to symptom onset was 16.2 months, with the earliest at 3 months and the latest at 6 years.⁵ In the same study, the reported sites were the zygomatic cheek (21.9%), temple (15.1%), chin (13.7%), and nasolabial fold (13.7%).⁵
The incidence of delayed-onset nodules is reported at under 1%, with proposed causes including hypersensitivity, foreign body reaction, injection placement, infection, sterile abscess, and biofilm formation.⁷ An international consensus recommendation describes infection or activation of dormant biofilm, and shifts in immune balance due to autoimmune disease or viral infection, as possible contributors.⁸ A systematic review has also collected cases triggered after viral infection or vaccination.⁹
Even if considerable time has passed since treatment, a new lump or recurrent swelling should be reported to the treating clinic.
What Should You Check Before Treatment?
Three things: product information, your own treatment history, and the clinic's emergency preparedness.
1. Confirm the product name and composition. You can check whether it is HA or non-HA and what areas it is approved for. The MFDS has advised patients to consult thoroughly with a physician about product characteristics and adverse effects beforehand, following reports of blindness and infection arising from use outside the approved intended purpose.²
2. Report your previous treatment history accurately. When, where, and what type you received directly affects the dose chosen this time. Additional injection without accounting for residual filler can lead to accumulation.
3. Confirm that emergency management is available. Whether hyaluronidase is kept on hand and whether a protocol exists for vascular complications is a more practical criterion than reviews.
The MFDS recommends recognizing that filler treatment is a medical procedure, receiving it from an experienced physician, and checking the labelling or package insert of the product to be used.¹
Frequently Asked Questions
Q. Are fillers a reliably effective procedure?
A. Randomized controlled trials of nasolabial folds have repeatedly demonstrated wrinkle improvement and satisfaction.¹⁰ In one 24-month study, improvement was sustained in over 90% of patients at 12 months, and satisfaction at 24 months was 72.4–81.7%.¹¹ Results still vary by area, product, injected volume, and individual factors.
Q. Are fillers and botulinum toxin the same procedure?
A. No. A filler is a medical device that physically fills a depleted area, whereas botulinum toxin is a pharmaceutical that blocks neuromuscular transmission. Their purpose, mode of action, and regulatory classification all differ.¹
Q. If a filler is dissolved, does everything return to how it was?
A. HA filler can be broken down with hyaluronidase, but degradation may be incomplete when the material has aggregated into a large bolus, is encapsulated, or when the enzyme does not diffuse sufficiently. Multiple sessions are sometimes required.
Q. Are non-HA fillers dangerous?
A. Rather than being dangerous, they differ in that the means of reversal are limited. Collagen-stimulating products offer gradual, longer-lasting results, but if a nodule forms or placement is inappropriate, the material cannot be removed enzymatically.
Q. How long does swelling last after filler treatment?
A. This varies between individuals; reactions such as swelling and bruising listed by the MFDS are generally observed from immediately after treatment for several days.¹ Swelling or nodules newly appearing more than two weeks later may represent a delayed reaction and warrant separate assessment.⁵
Q. Is it safe to have fillers repeatedly?
A. Repeat treatment is not itself a problem, but dosing needs to account for the possibility that previous filler remains. Given that MRI studies detected residual filler in all patients at two years,³ accurately sharing the timing and location of previous treatments is important.
Q. Which symptoms after treatment require immediate medical attention?
A. Severe pain during or immediately after treatment, skin colour change (pallor or purple discoloration), and visual disturbance may indicate a vascular complication and require immediate contact.⁶ Lumps or recurrent swelling appearing later should also be assessed.⁵
References and Sources
1. Ministry of Food and Drug Safety (MFDS), Republic of Korea. Safe Use Information for Cosmetic Dermal Fillers. https://www.mfds.go.kr/brd/m_465/view.do?seq=27164
2. MFDS. Approved intended use of cosmetic dermal fillers; product-specific approvals searchable via the medical device e-application portal. https://emedi.mfds.go.kr
3. Hyaluronic Acid Filler Longevity in the Mid-face: A Review of 33 Magnetic Resonance Imaging Studies. Plast Reconstr Surg Glob Open. https://journals.lww.com/prsgo/fulltext/10.1097/gox.0000000000005934~hyaluronic-acid-filler-longevity-in-the-mid-face-a-review-of
4. Longevity and Volume Expansion of Hyaluronic Acid Dermal Fillers: A Cross-sectional 3-dimensional Magnetic Resonance Imaging Study. Plast Reconstr Surg Glob Open. https://www.ovid.com/jnls/prsgo/fulltext/10.1097/gox.0000000000007894~longevity-and-volume-expansion-of-hyaluronic-acid-dermal
5. Biofilm formation is a risk factor for late and delayed complications of filler injection. PMC10800873. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10800873/
6. Wang R, Li Y, Li Z, Yao H, Zhai Z. Hyaluronic acid filler-induced vascular occlusion — three case reports and overview of prevention and treatment. J Cosmet Dermatol. 2024;23(4):1217-1223. https://pubmed.ncbi.nlm.nih.gov/38131127/
7. Case report and literature review of late inflammatory reactions to hyaluronic acid filler. Aesthetic Medicine. 2024.
8. Late-Onset Reactions after Hyaluronic Acid Dermal Fillers: A Consensus Recommendation on Etiology, Prevention and Management. PMID 38907876. https://pubmed.ncbi.nlm.nih.gov/38907876/
9. Systematic Review of Post-Viral Delayed Inflammation Associated with Hyaluronic Acid Dermal Fillers. PMC12565858. https://pmc.ncbi.nlm.nih.gov/articles/PMC12565858/
10. Efficacy and Safety of Two Resilient Hyaluronic Acid Fillers in the Treatment of Moderate-to-Severe Nasolabial Folds: A 64-Week, Prospective, Multicenter, Controlled, Randomized, Double-Blinded, Within-Subject Study. https://pubmed.ncbi.nlm.nih.gov/32217842/
11. Moers-Carpi MM, Sherwood S. Polycaprolactone for the Correction of Nasolabial Folds: A 24-Month, Prospective, Randomized, Controlled Clinical Trial. Dermatol Surg. 2013. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3615178/
12. Yazdanparast T, et al. Safety and Efficacy Assessment of a Cross-linked Hyaluronic Acid Dermal Filler for Correction of Moderate-to-Severe Nasolabial Folds in Skin Types III and IV. Dermatologic Therapy. 2024. https://onlinelibrary.wiley.com/doi/full/10.1155/2024/8487221
13. Safety and Potential Complications of Facial Wrinkle Correction with Dermal Fillers: A Systematic Literature Review. PMC11766492. https://pmc.ncbi.nlm.nih.gov/articles/PMC11766492/
14. Permanent Complications After Dermal Fillers: Risks, Prevention, and Management Strategies. Aesthetic Plastic Surgery. https://link.springer.com/article/10.1007/s00266-026-05989-8
15. U.S. Food and Drug Administration. FDA Executive Summary, General Issues Panel Meeting on Dermal Fillers. https://www.fda.gov/media/146870/download
This content is provided for general medical information purposes and does not guarantee the outcome of any specific treatment. Treatment decisions should be made following an in-person consultation with a medical professional.
Lieul Dermatology Clinic