What It Means to Dilute CaHA — Not Making It Weaker, Making It Reach Further

A CaHA product such as Radiesse does two things at once. The gel carrier adds volume immediately, and the microspheres inside it stimulate collagen over the following months.

But there are places — the neck, the décolleté, the back of the hands — where adding volume is exactly what you do not want. You want the collagen response without the filling. Dilution is how that is done.

The problem is that patients are almost never told about it. What gets said at the consultation is usually "we'll use Radiesse," and what does not get said is that the same product, at a different dilution, is effectively a different treatment. That is why one person says "I had Radiesse and it left a lump" and another says "I had Radiesse and nothing happened at all." Both can be true.

This column separates what has been shown from what is simply common practice. It does not arrange that line to our advantage.

A 2023 study set the floor for this discussion. Researchers injected CaHA diluted 1:1 and 1:2 into human abdominal tissue segments to see how it spread, and separately incubated cultured fibroblasts with CaHA at different concentrations to see what they produced.

• The 1:2 dilution spread further through the tissue and lowered the local concentration compared with 1:1.
• In culture, only the fibroblasts in direct contact with CaHA increased type III collagen expression.
• The amount each cell expressed was the same regardless of dilution.

The third point is the one that matters. People assume a diluted product stimulates more weakly, but from the cell's point of view there was no gradient — only contact or no contact. Which means that spreading the same quantity of product across more cells is the sensible thing to do. Dilution is a question of distribution, not of economy.

It is worth being precise about what this study is. It looked at tissue segments and cultured cells, not at faces months later. It explains a mechanism; it does not prove an outcome.

The most cited reference point is a 2017 study of the neck and décolleté. Twenty people received CaHA diluted with preserved saline, with biopsies at baseline, four months and seven months.

• 1:2 for normal skin, 1:4 for thin skin, 1:6 for atrophic skin.
• Type I collagen rose significantly at four months (p<0.05) and seven months (p<0.00001).
• Type III collagen rose sharply at four months (p<0.00001), then fell by seven months but stayed above baseline.
• Elastin and angiogenesis also rose at both time points. This is not a collagen-only effect.
• The tissue findings matched cutometry measurements of elasticity and pliability, and ultrasound measurements of dermal thickness.

A practical guidance paper from twelve expert injectors and a 2026 review repeated the same ranges and extended the approach beyond the face to the arms, abdomen and buttocks.

Here is where honesty is required. Those ratios — 1:2, 1:4, 1:6 — were not arrived at by comparing them. The 2017 study assigned a ratio according to skin thickness and reported the twenty participants pooled. It never asked which ratio was better.

And the two datasets that did compare ratios point the other way. One examined six dilutions in a single patient's thigh with biopsy at 90 days and found total collagen highest at 1:1 — with 2% lidocaine, not saline, as the diluent. The other was a porcine study with a negative control, reporting that the effect was more pronounced up to a 1:3 dilution.

So the accurate statement is this. Dilution itself has a mechanism and a safety argument behind it. But we found no human comparison showing that 1:4 or 1:6 outperforms 1:2, and what comparative data exist point in the opposite direction. Using thinner dilutions is closer to a practical judgment about avoiding clumping in thin skin than a conclusion from evidence.

The ratio is chosen from skin thickness and site, not from age. The same person has thin skin on the neck and thicker skin on the cheek. This is not something to request by number.

In the published work, the diluent is saline or lidocaine. The 2018 paper summarising East Asian practice says the same. Lidocaine reduces discomfort during the injection; saline keeps the mixture simple.

Mixing CaHA with hyaluronic acid is a different proposition, and section 5 deals with it separately.

This part is rarely discussed, and for patients it may be the most important thing here.

A 2025 study used an artificial arterial perfusion model to measure how differently diluted CaHA behaves if it enters a vessel.

• Undiluted CaHA-CMC was highly cohesive and tended to occlude proximally.
• Diluting it significantly reduced the average embolic particle size (p<0.0001) and completely eliminated its capacity for proximal occlusion (p=0.002).
• Among published cases of CaHA-related ischaemic injury, hyperdiluted product accounted for only 3%, and those largely followed a self-limited course.

So dilution is not only a choice about skin quality. It is also a choice that reduces the size of the problem if something goes wrong. This was a laboratory model rather than a human vessel, and dilution does not make vascular complications impossible. But it does make it hard to treat dilution as a matter of taste.

Combining CaHA with HA is genuinely done and there is literature behind it. The aim, though, is not the same as in section 2.

• A retrospective review of 41 patients treated with a premixed CaHA and cohesive polydensified HA in the midface and jawline reported that every patient improved by at least one grade at three months, 85% still did at twelve months, and no adverse events were recorded.
• There is now a commercial premixed product, with a retrospective series of 129 patients.
• A pilot of 15 patients combined CaHA, a botulinum toxin and HA in the same syringe for the neck.

These are largely volume and lifting protocols, and they are retrospective or uncontrolled. We could not find a study that directly tests hyaluronic acid as the diluent for biostimulatory hyperdilution. That many clinicians do something and that evidence exists for it are two different statements.

The first thing anyone should know before agreeing to CaHA is this: hyaluronidase does not dissolve it. An HA filler can be reversed in ten minutes if the result is wrong. CaHA has to be waited out. That single fact should change how carefully you choose an injector and how conservative you ask them to be.

Two recent findings soften this slightly.

First. A survey of 55 collagen-biostimulator complications in Brazil found that 89% were nodules and 60% appeared more than a month after treatment. Saline, hyaluronidase, dilute corticosteroid and energy devices were all used, and only 5 of the 55 resolved completely. Within that, hyaluronidase was of benefit only where CaHA had been used together with HA (p<0.01). That gives the practice of mixing with HA one real clinical argument: it leaves a partial route back. The evidence is a 55-case survey, not a trial.

Second. A case report described injecting saline into a non-inflammatory CaHA nodule to create a hyperdilution in place, then applying focused mechanical vibration with topical microneedling to redisperse the particles. The nodule became visibly smaller. This is one case, so it is not an established technique.

In short, "it cannot be dissolved" still stands. But it is not entirely beyond reach, and how much reach there is depends on what it was mixed with in the first place.

• You do not need to ask for a specific ratio. Dilution is decided from the site and the thickness of your skin. Arriving with a number can push the choice in the wrong direction.
• You do not need to bring up the "160% increase in collagen" figure. It is quoted everywhere, but tracing it back leads to a single patient's thigh, and the number does not appear in the original paper.
• You do not need to decide in advance how many sessions it should take to see something. The collagen response continues for months after the last treatment.

• If the treated area turns white or develops a mottled, net-like pattern, and the pain increases — call at once, whatever the hour.
• If a lump appears more than a month afterwards. Delayed nodules are not rare, and there are more options when they are seen early.
• If there is persistent or returning warmth and redness at the treated area.

Diluting CaHA is not a way of making the product go further. It is a matter of distribution — reaching more cells with the same material — and, as a side effect, of reducing the scale of a vascular event. The published ratios are 1:2 for normal skin, 1:4 for thin skin and 1:6 for atrophic skin, and the diluent in that work is saline or lidocaine. Mixing with HA has literature behind it, but with a different aim and a different quality of evidence. And the fact that CaHA is not dissolved by hyaluronidase is a condition to understand before starting, not after.

Which is why, at a consultation, "what ratio are you diluting to, and why that ratio for my skin" is a more useful question than "do you use Radiesse."

Dr. Chihak Lee, Director, Miso Clinic

4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, South Korea (Exit 1, Kyungpook National University Hospital Station)

+82-53-428-2700 · www.clinicmiso.co.kr

• We found no study directly testing hyaluronic acid as the diluent for biostimulatory hyperdilution.
• We found no randomised comparison of dilution ratios in humans. Whether 1:2 or 1:4 gives the better result is not something the evidence can answer, and the two comparative datasets that exist — one biopsy in a single patient, one porcine study — point toward the more concentrated end.
• The regulatory file for Radiesse in Korea is withheld from public release, so we could not read the original document.