Permanent vs Dissolvable Filler: Comparing Embolism Risk

A 2019 laboratory study in rabbits compared what happens when a permanent filler (polymethyl methacrylate, or PMMA) and a hyaluronic acid filler are injected directly into an artery. In this model, the hyaluronic acid filler caused more blockage and more skin damage at the same volume. The findings are interesting, but they come from animals, the study was funded by the maker of the permanent product, and it did not test hyaluronidase, the enzyme that can dissolve hyaluronic acid. For patients, the more practical message is that injection technique and small volumes matter for every filler.

Why this was studied

Vascular occlusion, where filler enters or presses on a blood vessel and blocks blood flow, is one of the most serious filler complications. It is rare, but it can damage skin and, very rarely, affect vision. Researchers want to know whether some fillers are more likely than others to cause a blockage once they reach a vessel.

PMMA filler contains tiny plastic microspheres suspended in a carrier gel. It is designed to be long-lasting and cannot be dissolved. Hyaluronic acid filler is a gel that gradually breaks down and can be dissolved with hyaluronidase.

What the researchers did

The team used the ears of white rabbits, a common model for studying blood flow in skin. They injected either 0.1 ml or 0.2 ml of PMMA or hyaluronic acid filler directly into the central ear artery, then watched blood flow, looked for filler travelling backwards in the vessel, and checked for skin damage a week later. Tissue was also examined under a microscope.

What they found

At the same volume, the hyaluronic acid filler behaved worse in this model:

• All hyaluronic acid injections caused a sustained blockage, compared with fewer than a third of PMMA injections.
• Hyaluronic acid was much more likely to travel backwards past the injection point.
• Skin damage was more frequent and covered a larger area in the hyaluronic acid groups.

Doubling the volume increased blockage and skin damage for both fillers. The authors concluded that, at equal volumes, PMMA carried less embolism risk in this model, and that large single-site injections should be avoided in favour of slow, small amounts.

How strong is this evidence?

This is an animal study, and that shapes how much weight it can bear. Important limits include:

• Rabbits are not people. Rabbit ear vessels differ in size and structure from human facial vessels.
• The injections were deliberately placed inside an artery. In real practice, the goal is to avoid vessels altogether, and many protective steps are taken to do so.
• No treatment was tested. The study did not use hyaluronidase, so it could not show what happens when a hyaluronic acid blockage is dissolved promptly, which is standard emergency care.
• Small groups and one late check. Each group had 10 to 20 ears, and outcomes were measured at a single time point.
• Funding. The study was funded by the manufacturer of the PMMA product tested.

So the study tells us how two materials behaved in one artificial worst-case scenario, not which filler is safer for patients overall.

Why might the fillers behave differently?

The authors offer some possible explanations, though they were not directly tested. Hyaluronic acid gel is soft and cohesive, so it may travel along a vessel as a continuous column and spread into smaller branches. PMMA consists of firm microspheres in a carrier gel, and the spheres may lodge in place rather than flowing onward. Differences in thickness, particle size and how the product spreads under pressure may all play a part. These ideas help explain the results in rabbits, but they remain speculation until tested in further research.

Why reversibility still matters

A key difference between these fillers is what can be done if something goes wrong. Hyaluronic acid can be broken down with hyaluronidase, and physician-led clinics keep it on hand with an emergency protocol. PMMA and other permanent fillers cannot be dissolved, so complications such as lumps or blocked vessels may need surgery or other treatment and can be harder to reverse.

Long-lasting fillers also carry their own risk of delayed lumps and granulomas years later. Our articles on vascular occlusion safety and dissolving filler explain these issues in more detail.

What it means for you

This study does not change the basics of filler safety. Whatever product is used, the measures that lower risk are similar:

• A trained injector with a detailed knowledge of facial anatomy
• Small amounts injected slowly, especially in higher-risk areas
• Appropriate choice of needle or cannula for the area
• An emergency plan, with hyaluronidase available when hyaluronic acid is used

Know the warning signs. Seek help immediately for skin that turns pale, dusky or mottled, severe or worsening pain during or soon after an injection, or any change in vision.

Questions to ask at your consultation

• Is the product dissolvable, and what is the plan if a blood vessel is affected?
• How do you reduce the risk of injecting into a vessel in this area?
• What are the long-term risks of a permanent filler compared with a temporary one?

Frequently asked questions

Does this mean permanent filler is safer?

Not on its own. The study used rabbits, direct injection into an artery and no treatment. Permanent fillers cannot be reversed and have their own long-term risks, which this study did not examine.

How common is vascular occlusion?

It is rare. Careful technique, anatomy knowledge and small volumes lower the risk further, and prompt treatment improves outcomes.

Can I find out what filler I had in the past?

Ask the clinic that treated you for your records. Knowing whether a product was dissolvable helps any future physician.

If you are comparing filler options or have questions about safety, HealthPark Medical Aesthetics can explain the trade-offs in a consultation, including when no treatment may be the better choice.

Source

Nie F, Xie H, Wang G, An Y. Risk comparison of filler embolism between polymethyl methacrylate (PMMA) and hyaluronic acid (HA). Aesthetic Plastic Surgery, 2019. Read the study