Hyaluronidase guide: dissolving HA filler safely and the emergency vascular protocol

Hyaluronidase is an enzyme that degrades hyaluronic acid (HA) by cleaving the glycosidic bonds between HA saccharide units. In aesthetic medicine, it is the reversal agent for HA-based dermal fillers — dissolving misplaced, overfilled, or complicated filler. It is also the emergency treatment for vascular occlusion, one of the most serious complications of filler injection. Here is a complete guide.

The mechanism: enzymatic HA degradation

How hyaluronidase works

Hyaluronic acid is a polysaccharide — a long chain of repeating disaccharide units (glucuronic acid + N-acetylglucosamine) linked by glycosidic bonds. Cross-linked HA filler products add BDDE cross-links between HA chains, creating the gel structure that resists enzymatic degradation and provides longevity.

Hyaluronidase cleaves these glycosidic bonds, breaking the HA polymer into smaller fragments that are then cleared by normal tissue metabolism. With sufficient hyaluronidase:
The HA filler gel is enzymatically dissolved
Fragments are cleared over 24–72 hours
The tissue returns toward its pre-filler state

Cross-linked filler requires more hyaluronidase: More cross-linked HA products (Juvederm Voluma, Restylane Lyft) are more resistant to enzymatic degradation than lightly cross-linked products (Restylane Silk, Juvederm Ultra). Higher doses or multiple sessions may be required for dense, highly cross-linked fillers.

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Hyaluronidase products

Bovine-derived (Vitrase, Wydase)

Traditional hyaluronidase products are derived from bovine (cow) testes. Widely available and less expensive; however:
Higher allergenicity — bovine-derived hyaluronidase has greater potential to cause allergic reactions, including rare anaphylaxis
Variable activity and purity between products
Allergy testing before elective dissolution (skin prick test) is recommended by many providers

Recombinant human hyaluronidase (Hylenex — halozyme)

Hylenex is a recombinant human hyaluronidase — engineered from human protein, not animal-derived. Lower allergenicity than bovine products. Preferred by many providers for elective filler dissolution; standard for emergency vascular occlusion protocols where time does not permit allergy testing.

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Indications for dissolving filler

Elective dissolving

Aesthetic dissatisfaction: Overcorrection, asymmetry, unnatural appearance, or migration of previously placed HA filler.

Filler migration: HA filler can migrate over time from the injection site — particularly around the lips, where chronic muscle movement can carry filler into the perioral area producing a "pillow" or "duck" appearance.

Tyndall effect: Superficially placed HA filler in thin-skin areas (tear trough, periorbital) can produce a blue-gray discoloration from the Tyndall light-scattering effect. Hyaluronidase dissolves superficial filler to resolve the discoloration.

Prior to retreatment: Some providers dissolve accumulated or layered prior filler before placing fresh product to ensure optimal starting anatomy.

Emergency dissolving — vascular occlusion

The most critical indication. Vascular occlusion occurs when filler is inadvertently injected into or compresses an artery, blocking blood flow to tissue. Downstream ischemia → necrosis within hours if untreated. Signs:

Immediate blanching (whitening) of the skin downstream from the injection site
Dusky gray or mottled color progressing over minutes to hours
Severe pain at or beyond the injection site
Skin that does not blanch with pressure (vasospasm resolved)

This is a medical emergency. The window for preventing tissue necrosis with hyaluronidase is narrow — treatment within 1–4 hours has the highest probability of complete reversal.

Emergency vascular occlusion protocol:
Immediately administer high-dose hyaluronidase (typically 150–1500 units or more, depending on the protocol and lesion extent) directly into and around the area of suspected occlusion — not just at the injection site
Aspirate and apply warm compresses to promote vasodilation
Reassess every 30–60 minutes; if no improvement within 60–90 minutes, repeat dosing
If occlusion involves the ophthalmic artery (vision changes, globe pain), immediate ophthalmology consultation and retrobulbar hyaluronidase injection may be indicated
Do not wait for results — vascular occlusion warrants immediate, aggressive, repeated dosing

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Standard elective dosing

Dosing for elective filler dissolution varies significantly by location and filler density:

| Location / Indication | Typical Starting Dose | Notes |
|---|---|---|
| Lips (mild overcorrection) | 10–30 units | Start conservative; re-evaluate at 24–48h |
| Lips (significant volume/migration) | 50–150 units | May require multiple sessions |
| Tear trough (Tyndall) | 10–30 units | Very conservative; thin skin, risk of over-dissolving |
| Nasolabial fold | 20–50 units | Standard |
| Cheek (superficial HA) | 30–75 units | Deeper, more cross-linked filler needs higher doses |
| Cheek (deep volumizer, Voluma) | 75–200 units | Multiple sessions often required |
| Nose (liquid rhinoplasty) | 20–60 units | Conservative; anatomically complex |
| Emergency vascular occlusion | 150–1,500 units | No dose ceiling in emergency; use what is needed |

Dilution: Hyaluronidase is typically diluted in normal saline for injection. Concentration varies by provider protocol — 10–75 units/mL for elective; higher for emergency.

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What to expect after dissolving

Timeline

24 hours: Most HA filler is dissolved within 24 hours of an adequate hyaluronidase dose. Partial dissolution may be evident sooner.

24–72 hours: Continued clearance of HA fragments; tissue settles into the dissolved state.

2 weeks: The standard wait before retreating with new filler. This allows complete clearance of both the dissolved HA and residual hyaluronidase activity, ensuring the new filler is placed in a clean tissue environment.

Post-dissolving appearance

Swelling: Hyaluronidase injections cause significant temporary swelling — the enzyme disrupts local tissue and the inflammatory response + filler dissolution produces edema. Swelling peaks at 24–48 hours and resolves within 3–5 days.

Bruising: Injection-related bruising; resolves in 5–10 days.

Apparent "over-correction": The swelling from hyaluronidase itself can create temporary volume during the first 24–48 hours, followed by collapse as both swelling and filler clear. Patients must be counseled not to assess final results for 1–2 weeks.

The "hollowed" period: After dissolving, the pre-filler anatomy — including any volume loss that prompted the original filler treatment — returns. Patients may feel they look worse than before filler. This is temporary; retreatment after 2 weeks restores volume appropriately.

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Allergy and safety

Allergy testing (bovine products): For elective dissolving with bovine hyaluronidase, a skin prick test (intradermal 0.02 mL of diluted product; observe 30 min) identifies immediate hypersensitivity. Skip in true emergency — the risk of anaphylaxis is outweighed by the risk of tissue necrosis.

Anaphylaxis risk: Very rare (estimated < 0.1%) with bovine products; lower with recombinant. Any provider using hyaluronidase should have epinephrine and anaphylaxis management supplies immediately available.

Over-dissolving: Hyaluronidase degrades native HA in the dermis in addition to filler — particularly with high doses or repeated sessions. The native HA loss is temporary (dermis replenishes endogenous HA within 4–6 weeks), but patients may experience additional deflation beyond the dissolved filler volume in the immediate post-treatment period.

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What hyaluronidase cannot dissolve

Hyaluronidase only dissolves hyaluronic acid. It has no effect on:
Calcium hydroxylapatite fillers (Radiesse) — not HA-based; no reversal agent exists
Poly-L-lactic acid (Sculptra) — no reversal agent; management of complications is supportive
Silicone — permanent; surgical removal only
Fat grafts — autologous tissue; not dissolved by hyaluronidase

Patients asking about dissolving non-HA fillers should be counseled that hyaluronidase is not effective and alternative management must be discussed.

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