Hyaluronidase:
what it dissolves, how long it takes and its side effects

Told your filler cannot be dissolved, and only offered surgery? Get assessed first

Hyaluronidase acts on hyaluronic acid only. When a filler is something else, patients are often told it cannot be dissolved and that surgery is the only way to take it out. The first half is true. Material that cannot be dissolved can still be treated without an incision. Before you agree to an operation, know what it means:

• A scar. Every cut through the skin of the face heals with a scar.
• A dent. Cutting out a lump takes tissue with it, and the area can heal hollow or uneven.
• Nerve injury. Nerves that give the face feeling and movement run close to where filler sits. An injured nerve can leave numbness, or weakness in a smile, a lip or a brow.
• Product left behind. Filler spread through tissue is hard to remove completely.
• No way back. Tissue that has been cut out cannot be put back.

Dr Sin Yong maps the filler with ultrasound, dissolves hyaluronic acid, and treats material that cannot be dissolved, including collagen stimulators, silicone and other non-absorbable fillers, with the Sculpting mode of Time Freeze Laser LCLR®, without an incision. In Dr Sin Yong's practice, almost every hard lump is treated without surgery. If yours is one of the few that needs surgery, you are told plainly, and why.

What hyaluronidase is, and what it acts on

Hyaluronidase is an enzyme that breaks the long chains of hyaluronic acid into small fragments that the body clears. It has been in medical use since 1949 and is the agent used to dissolve hyaluronic acid filler (Murray 2021). Filler gel is cross-linked so that the body's own enzymes break it down slowly; injected hyaluronidase breaks it down quickly. A short definition is in the glossary under hyaluronidase.

It acts on hyaluronic acid and nothing else: not polycaprolactone, poly-L-lactic acid, poly-D,L-lactic acid, calcium hydroxylapatite, silicone or fat. Poly-lactic acid and calcium hydroxylapatite are broken down by the body through other, slower processes, and non-absorbable fillers stay; a medical treatment described for calcium hydroxylapatite acts slowly and is not effective in an emergency (Wollina 2024). Polycaprolactone fillers cannot be removed straight away by injecting an enzyme (Lin 2020). In a series of 55 complications after collagen stimulators, hyaluronidase helped only where calcium hydroxylapatite had been combined with hyaluronic acid (Ianhez 2024).

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“Dissolving filler is not an undo button.”

Dr Sin YongOn what dissolving can and cannot do

Why different hyaluronic acid fillers respond differently to the same dose

Hyaluronic acid fillers are not all made the same way, and the enzyme does not break them all down at the same rate (Landau 2015). The evidence on how fast, and with how much enzyme, comes from laboratory, animal and small human studies:

• Manufacturing technology. In a laboratory comparison of 16 fillers made with 6 manufacturing technologies, fillers made with one manufacturing technology were the hardest to break down and those made with another the easiest. Manufacturing technology was the most important factor in how reversible a filler was (Faivre 2024).
• Dose response in people. In a prospective, randomised, masked study in 9 people, using small test deposits of three fillers, a cheek-volumising filler barely changed at the lowest dose and needed more than the highest dose tested, while another filler responded even to the lowest dose (Zhang-Nunes 2021).
• Filler structure. In laboratory and animal work, biphasic fillers dissolved faster at lower enzyme concentrations, while monophasic fillers needed higher concentrations and longer exposure (Hong, J Cosmet Dermatol 2025).
• High enough doses. In a rat study of three fillers, the highest doses tested caused complete loss of projection for all of them, lower or diluted doses less, and four weeks of settling into the tissue did not change how they broke down (Shumate 2018).

Most of this evidence shows that fillers differ in how much enzyme they need, while the animal study found that high enough doses broke down all three fillers tested. That is why the dose is titrated to effect rather than set in advance (King 2018), why low to moderate doses are favoured for non-urgent problems (Kroumpouzos and Treacy 2024), and why knowing what was injected, or seeing it on a scan, matters. The trial evidence is thinner than many people assume: a 2024 scoping review found just five randomised trials, in 53 subjects and on arm or back skin, supporting hyaluronidase for hyaluronic acid nodules, and no trial evidence for facial reversal or over-correction (Borzabadi-Farahani 2024).

How long does hyaluronidase take to work?

It starts acting soon after it is injected. In the randomised study above, the largest change came between 30 minutes and 3 hours after the injection, with gradual further breakdown up to week 2 (Zhang-Nunes 2021). In laboratory and animal work, the enzyme's activity in tissue fell off within 30 minutes, and injecting it directly into the filler worked better than applying it over the surface (Hong, J Cosmet Dermatol 2025). Where the enzyme is placed matters, not only how much.

The injections themselves cause some swelling, so the change is not judged on the day. Dr Sin Yong reviews the area at about 48 hours and decides any further dose then, based on what remains. He waits at least two weeks after hyaluronidase before any refilling.

Ultrasound-guided placement: putting the enzyme where the filler is

Because the enzyme acts where it is placed, and not for long, it needs to go into the filler itself. Dr Sin Yong scans the area himself with high-frequency ultrasound before any dissolving. Under ultrasound guidance, hyaluronidase can be injected directly into the filler deposit (Schelke 2018), and an expert review notes that guidance can make these treatments more effective (Kroumpouzos and Treacy 2024).

What the scan shows

• Where the filler sits and how deep: under the skin, in the fat, in the muscle or on the bone.
• How much there is, and whether there is one deposit or several from different treatments.
• What the material is likely made of: hyaluronic acid, a collagen stimulator or something else.
• The blood vessels nearby, which guide the path of the needle.
• Whether the fullness is filler at all, or swelling, fluid or your own tissue.

The step-by-step detail is on ultrasound-guided filler dissolving.

Planned dissolving: skin test, a small first dose, review at about 48 hours

1. History. What was injected, where and when; any earlier hyaluronidase and any reaction to it; and bee or wasp sting allergy, which guidance lists as a reason for extra care (Murray 2021).
2. Ultrasound. The filler is mapped before anything is injected.
3. Skin test. Before planned dissolving, Dr Sin Yong always does a skin test: a small amount of hyaluronidase is injected just under the skin to check for a reaction. This is done before any planned dissolving.
4. A small first dose. Placed into the mapped filler with a fine needle and titrated to effect rather than given as a set number of units (King 2018), with a low dose into the excess for a non-urgent problem (Landau 2015).
5. Review at about 48 hours. Further doses only where filler remains.

Dissolving more than the excess

The enzyme does not tell injected filler from the hyaluronic acid your skin makes itself, and it does not stop at the edge of the excess. Dissolving more than the excess can leave a hollow, especially where filler was hiding a groove or loose skin. That is why the dose is small and staged, and aimed at the excess rather than everything.

Refilling

Not on the same day. Dr Sin Yong waits at least two weeks after hyaluronidase before any refilling. Whether to add anything back is decided then, and sometimes the answer is to leave the area as it is.

Before you book

• Pregnancy and breastfeeding: non-urgent dissolving is usually deferred.
• An infection or a cold sore near the area is settled first.
• Bring product names, dates and any clinic notes if you have them. If you do not, the assessment still goes ahead.

Emergencies: a blocked blood vessel is treated at once

A blocked blood vessel after hyaluronic acid filler is a different situation from planned dissolving. It is treated straight away with high doses of hyaluronidase under a separate protocol, not with the small, staged doses described above (Murray 2021; Landau 2015; Kroumpouzos and Treacy 2024). Treatment is not delayed for a skin test: guidance advises testing before non-urgent dissolving, but not where a delay could cause harm (King 2018).

Urgent: a change in vision or eye pain after filler: call 995 now. Skin that turns pale, dusky or mottled, or pain that is getting worse, needs urgent assessment by the doctor who injected you, or at A&E, now. See the warning signs of a blocked blood vessel after filler.

Hyaluronidase side effects

• Swelling, redness, itch or bruising at the injection points. These are common and settle.
• A hollow where more than the excess was dissolved, which staged dosing is designed to avoid.
• Some of the skin's own hyaluronic acid near the injection points is broken down too; the body replaces it.
• Allergic reaction. Uncommon; usually local swelling and itch, rarely more serious.
• No effect on other fillers. Material that is not hyaluronic acid does not respond.

Hyaluronidase allergy

In a systematic review of 37 studies describing 106 patients with hyaluronidase allergy, previous hyaluronidase injections and sensitisation from insect or wasp stings were the main risk factors, many reactions happened at a second injection, and the reactions responded to treatment (Guliyeva 2024). Having had hyaluronidase before without a problem does not rule out a reaction next time. Swelling or itching that spreads beyond the treated area, or hives, needs a call to the clinic straight away. Breathing difficulty, a tight throat, or spreading swelling of the face, lips, tongue or throat means calling 995 now. More is in hyaluronidase allergy and the skin test.

When hyaluronidase is not the first step

• A red, hot or tender lump. This may be infection. Consensus recommendations advise hyaluronidase for non-inflammatory reactions without active infection; an infection needs drainage, a sample for testing and medical treatment, not hyaluronidase as the first step (Baranska-Rybak 2024).
• Recent filler. Early swelling and unevenness often settle on their own, so a review is usually wiser than dissolving straight away, unless there are signs of a blocked vessel.
• Fullness that is not filler. Swelling, fluid, weight change and your own tissue can look like filler, and the enzyme does not act on them.
• Filler that is not hyaluronic acid. The enzyme has nothing to act on; what is done instead is set out below.
• Dissolving that has already failed. The enzyme may not have reached the filler, the filler may not be hyaluronic acid, or the fullness may be something else. See when filler dissolving has not worked.

When the lump is not hyaluronic acid: the Sculpting mode, without an incision

When the scan shows that a lump or an excess is a collagen stimulator, silicone or another non-absorbable filler, more hyaluronidase is not the answer. Dr Sin Yong treats this material with the Sculpting mode of Time Freeze Laser LCLR®, for nodules large and small, without an incision. Silicone and other non-absorbable fillers are included. Where hyaluronic acid sits together with other products, the hyaluronic acid is dissolved first and the Sculpting mode is used for what remains, in a planned order.

The laser has its own risks, including blistering or a change in skin colour, so settings are chosen for your skin, and these are explained at the assessment. More is in the Sculpting mode of Time Freeze Laser LCLR® and hard lumps after filler or skin boosters.

Tried other treatments and almost given up?

Many patients who come to see Dr Sin Yong about filler that hyaluronidase has not dissolved tell him they have tried almost everything else and had given up hope. Having tried other treatments does not mean nothing more can be done: what is done next depends on what the scan shows.

That history is useful. Knowing what was injected, when, and what has already been tried often explains why a problem has stayed: hyaluronidase acts only on hyaluronic acid and only where it reaches, some fillers are not hyaluronic acid at all, and swelling or fluid can look like filler. Ultrasound helps show which of these applies, and the plan starts from there. For material that cannot be dissolved, Dr Sin Yong uses the Sculpting mode of Time Freeze Laser LCLR® for nodules large and small, without an incision. How each person responds varies.

If you have been told nothing more can be done, it is still worth having the area scanned: ultrasound helps show what is there, and the plan is made from that. Bring any records of past treatments, product names and dates if you have them. More on this is in when filler dissolving has not worked.

How Dr Sin Yong uses hyaluronidase

Dr Sin Yong takes the history, performs the ultrasound scan and the skin test, and places the enzyme himself on Orchard Road. The aim is to dissolve what is in excess, in stages, and to use the Sculpting mode of Time Freeze Laser LCLR® for what the enzyme cannot touch, rather than adding more filler to disguise a problem. He developed the Time Freeze Laser LCLR® protocol himself and has been invited to share his clinical expertise internationally, including as a Global Key Opinion Leader.

You do not need to have been treated here: filler placed elsewhere in Singapore or overseas is assessed in the same way. The wider guide is filler dissolving in Singapore.