What is the difference between filler and boosters

The first thing we checked while writing this article was the official definition of “what a skin booster is”. This is the result.

• The only paper that attempted to formally define and classify skin boosters was published in 2024 and then retracted.
• It is not a regulatory category. According to a review article, “the majority of injectable fillers are classified as class III medical devices regardless of composition”. Boosters and fillers sit in the same place.
• The US FDA approved an indication, not a category. The indication for one hyaluronic acid product approved in 2023 was improvement of “skin smoothness of the cheeks”. A new indication was created, not a new category.

There is one thing that has been defined. Ten experts from eight countries produced a consensus statement organising “skin quality” into four attributes — tone evenness, surface evenness, firmness and glow. However, this is expert opinion rather than evidence, and it does not define which products are boosters either.

So this article does not begin with “what is a booster”. That question has no answer. Instead we look at “what actually differs”.

Let us start with the clearest counterexample.

In other words, what determines the category is not the substance in the vial but how much it is diluted and which layer it is placed in. The same vial of Radiesse is used for volume treatments and for treating the skin of the neck.

There is an interesting case on the regulatory side too. One PDO powder product was approved by Korea's MFDS in 2021 as a ‘filler device’, yet the study evaluating it placed it in the nasolabial folds and measured roughness · elasticity · hydration · pores. A product licensed as a filler, in a filler location, measured with booster endpoints.

The explanation that “boosters are thin and fillers are firm” is also common. Looking at the actual measurements, it is not that simple.

The value that expresses the firmness of a gel is called G′. There is a study that measured three products classified as boosters under the same conditions.

There is one more thing. In a separate study, the G′ of a representative volumising filler was measured at 219.9 Pa. That is lower than Product A in the table above (430 Pa).

But we will be honest. The two figures come from different papers and different measurement conditions, so they must not be compared directly. We could not find a paper that measured fillers and boosters side by side under the same protocol. Even so, we can say that “boosters are thin” is not self-evident.

The explanation that “boosters are the non-cross-linked ones” does not hold either. All three products in the table above are cross-linked, and BYRYZN, which Miso Clinic uses, is cross-linked hyaluronic acid as well.

If it is not the material, what is different? The first answer is what the trials measured.

Organising the evidence for the boosters Miso Clinic uses by this standard gives the following.

And we will add this honestly. There are products for which no clinical trial naming the product exists — Rejuran Eye, Juvelook Volume, BYRYZN, DCLASSY, and Re2O · CellREDM individually. These end up being explained by borrowing the evidence for other products in the same family. We have written the same thing on our product pages.

We are often asked “which of the two is better”. The answer is that no trial exists that could answer that question.

Every comparison that exists is within the same category — filler against filler, or booster against booster. We could not find a trial that randomly allocated patients to compare a volumising filler with a skin booster.

The reason is simple. Because the primary endpoints differ, the design does not hold together in the first place. One side measures by wrinkle grade and the other by cutometer and water loss, and the two cannot be put on the same scale.

So “which is better” is the wrong question. The right question is “is my problem volume, or texture?” If your cheek has hollowed and casts a shadow, improving texture leaves the shadow where it was; if your skin is thin and rough, adding volume leaves the texture where it was.

We will also be clear about doing both together. We could not find a randomised trial combining filler and boosters. There are no trial data on order · interval · interaction. There is literature that mentions synergy, but that is the authors' hypothesis, not something tested.

We think this is the most important part for patients.

Hyaluronic acid can be dissolved. It is broken down by injecting an enzyme called hyaluronidase. However, the time required differs by more than twelvefold between products.

For anything that is not hyaluronic acid, there is no antidote.

Of the 10 boosters Miso Clinic stocks, only one, BYRYZN, is in the hyaluronic acid family. For the rest, no method of reversal is known. This is the practical reason we proceed “in stages, a little at a time”. When handling something irreversible, it is safer to start small and add.

We would add that even the protocol for using hyaluronidase in a vascular event has no randomised trial behind it. The recommendation to use a high dose of 450 to 1,500 units within 4 hours rests on expert consensus and observational studies.

Blindness is the most feared complication of filler treatment. The numbers have accumulated.

• 2019 review (48 new cases, 146 cumulative): the causative material was hyaluronic acid in 81.3% and CaHA in 10.4%. Sites were the nose 56.3%, the glabella 27.1% and the forehead 18.8%.
• 2024 review (365 new cases, a century of cumulative cases): hyaluronic acid 79.6%. Of the 318 cases with reported outcomes, full recovery 6.0%, partial 25.8%, no recovery 68.2%.
• The incidence is estimated at roughly 1 in 200,000 treatments, but under-reporting is certain. In large prospective studies, vascular complications overall were under 1% and early vascular injury about 0.07%.

The description of the most dangerous layer is this — “the safest planes are deep on bone or very superficial dermis, with the subcutaneous layer being the most dangerous location, where the vessels run”.

There is something here we must write honestly. The claim that “boosters are placed superficially, so there are no vascular events” is not true. There are counterexamples — a case has been reported of a 23-year-old whose retinal artery occluded within seconds of PDLLA being placed in the glabella (hyaluronidase does not work on PDLLA), and there is also a case of delayed vascular occlusion 48 hours later from a hyaluronic acid booster placed intradermally in 0.01mL portions. The risk is likely to be low, but no study has quantified it, and it is not zero.

We will also record the review's sentences on the non-hyaluronic acid family — “although reported less frequently, they were more often associated with severe ocular · neurological injury and were harder to reverse”, and “because there is no specific antidote, once an embolus forms it is difficult to remove”.

Delayed nodules were 0.33% in one single-centre retrospective study (2,139 patients) and 6.2% in a CaHA trial on the back of the hands. For PN · PDLLA · PCL · hADM we could not find a study with a denominator for the incidence of delayed nodules.

Translating the evidence so far into practice gives the following.

1. We first separate whether the problem is volume or texture. If there is shadowing and a hollowed look, it is a volume problem; if the skin is thin, rough and the pores stand out, it is a texture problem. We do not try to solve both with one treatment.
2. We do not answer “which is better”. Because there is no comparative trial. Instead we ask “what is bothering you”.
3. We tell you in advance whether it can be reversed. Nine of Miso Clinic's 10 boosters have no antidote. You should not begin without knowing this.
4. We proceed in stages. Because we are handling irreversible materials. That said, there is no trial directly comparing “staged is more natural”, so we state that this is our own approach.
5. We tell you the strength of evidence for each family. We do not present a family with a phase III randomised trial and a family with two case reports as carrying the same weight.
6. We are particularly careful with the nose and glabella. More than half of blindness cases involve the nose and a quarter the glabella.

A comparison of the 10 boosters is on the skin booster guide, and whether to do a booster or lifting first is covered in should I have a booster or a lifting treatment.

• What we confirmed — “skin booster” is not a regulatory category, and the only paper that tried to define it was retracted. Filler and boosters are generally the same class of medical device.
• What we confirmed — the same material changes category depending on dilution and the layer it is injected into. CaHA is the clearest example.
• What we confirmed — even among products classified as boosters, firmness differs by more than tenfold. “Boosters are thin” and “boosters are non-cross-linked” do not hold.
• What we confirmed — only hyaluronic acid can be dissolved, and it takes from 3.6 to 45.1 minutes depending on the product. CaHA · PDLLA · PCL · PN · hADM have no antidote.
• What does not exist — a randomised trial directly comparing filler and boosters, a study testing the two in combination, a study measuring the physical properties of the two families side by side under the same conditions, and a study measuring how long boosters persist in tissue by imaging.
• What is not true — “boosters are placed superficially, so there are no vascular events.” Counterexamples have been reported.

So the conclusion is that “filler and boosters are not different materials but different questions”. Whether you are asking about volume or about texture comes first, and after that comes “can this be reversed?” We strongly recommend asking that second question.

Written and reviewed by Lee Chi-Hak, MD, medical director of Miso Clinic in Daegu, South Korea. Every study cited above is given together with its design, its size and the limitations the authors themselves recorded, and where we could not find data, we have said that we could not find any.