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Every few months, there seems to be a new “collagen stimulator” in aesthetic medicine.
And I understand the appeal.
Instead of simply adding volume, these injectables promise to encourage our own tissues to produce more collagen. It sounds inherently regenerative—and therefore inherently good.
But there is a question I think we need to ask more often:
How are we stimulating that collagen?
Because collagen production is not automatically synonymous with healthy regeneration.
Scar tissue contains collagen.
Fibrosis contains collagen.
Chronic foreign-body reactions can involve collagen deposition.
So for me, the important question has never been simply:
“Does this product stimulate collagen?”
It is:
“What biological pathway are we asking the tissue to go through to produce it?”
And this is one of the main reasons that, despite the growing number of biostimulatory injectables available, calcium hydroxyapatite—or CaHA—remains my collagen stimulator of choice.
Calcium hydroxyapatite, or CaHA, is a bioceramic material with a long history of biomedical use.
In the CaHA formulation discussed in the regenerative-aesthetics literature, smooth CaHA microspheres are suspended within a carboxymethylcellulose, or CMC, gel. The gel initially provides support and then gradually dissipates, while the microspheres interact with the surrounding tissue.
But what interests me most is what happens afterwards.
Studies suggest CaHA can stimulate much more than collagen alone. Research has demonstrated changes involving type I and III collagen, elastin, proteoglycans, fibroblast activity, and angiogenesis.
That distinction matters to me.
Because youthful skin isn’t made of collagen alone.
One of the papers I have attached describes a concept in regenerative aesthetics that I think is particularly important.
When tissue heals, there are broadly two overlapping possibilities: regeneration and replacement.
Replacement essentially repairs an area with connective tissue. Regeneration aims, as far as possible, to restore the architecture and function of the original tissue.
These are not necessarily the same biological outcome.
The authors therefore argue that a truly regenerative aesthetic treatment should ideally improve both tissue structure and tissue function, rather than simply depositing more of one extracellular-matrix component.
This is where I think our language in aesthetics sometimes becomes too simplistic.
We say:
“This stimulates collagen.”
My response is increasingly:
“Yes—but what kind of tissue response did we create to get there?”
Macrophages are immune cells, but calling them simply “immune cells” dramatically understates what they do.
They are involved in inflammation, clearing cellular debris, coordinating repair and remodelling tissue.
Traditionally, macrophage activation has often been simplified into two phenotypes:
M1 macrophages are associated more strongly with a pro-inflammatory response. They can produce inflammatory mediators including TNF-α, IL-1β and IL-6.
M2 macrophages are associated more strongly with resolution, repair, remodelling and restoration of tissue homeostasis.
In reality, macrophages do not exist in two neat boxes. They occupy a spectrum of phenotypes and can change according to signals from their local environment. The M1/M2 framework is therefore best thought of as a useful way of understanding two ends of a much more complex biological continuum.
This is important.
I am not saying that M1 macrophages are bad and M2 macrophages are good.
We need inflammation.
An appropriate inflammatory response is fundamental to defence and healing. Without it, normal tissue repair would not occur.
The problem is persistent or excessive inflammation.
And this becomes particularly interesting when we are talking about ageing.
In my previous article, I discussed inflammaging: the chronic, low-grade inflammatory environment associated with biological ageing.
Ageing tissue is already biologically different from young tissue. Fibroblast numbers and activity decline, extracellular matrix becomes fragmented, oxidative stress accumulates, senescent cells alter their surrounding microenvironment, and pro-inflammatory signalling can increase.
So if I am treating ageing tissue, I find myself asking:
Do I necessarily want my regenerative strategy to depend heavily upon creating additional prolonged inflammation?
For me, increasingly, the answer is no.
One of the things I find most compelling about CaHA is that its proposed regenerative mechanism appears not to depend primarily on chronic inflammation.
The review you provided describes CaHA as relatively immunologically inert, with minimal immune-cell recruitment and activation. Histological studies cited in the review found either mild or scant inflammatory responses after implantation, while subsequent collagen formation still occurred.
That is fascinating.
Because it suggests that we do not necessarily need a large, persistent inflammatory reaction in order to stimulate extracellular matrix regeneration.
Instead, another important mechanism comes into play:
Mechanotransduction.
Fibroblasts don’t simply float passively inside our skin.
They interact physically with the extracellular matrix around them.
In youthful tissue, fibroblasts are appropriately stretched within a healthy collagen network. That mechanical tension influences how they behave.
As collagen becomes fragmented with ageing, fibroblasts lose some of that mechanical support. Their shape and mechanical signalling change, and their production of extracellular matrix proteins can decline. The regenerative-aesthetics paper describes this relationship between extracellular matrix integrity, fibroblast tension, and declining collagen synthesis with ageing.
CaHA microspheres appear to provide a scaffold with which fibroblasts can physically interact.
That interaction activates mechanotransduction—essentially converting a mechanical stimulus into cellular signalling.
The CaHA review describes collagen fibres arising around and connecting neighbouring microspheres, with CaHA-associated fibroblasts producing denser, more organised collagen networks. Importantly, the proposed mechanism centres substantially on direct fibroblast–microsphere interaction rather than requiring macrophages to drive the entire process.
I think of it almost like giving an ageing fibroblast something to hold onto again.
Different biostimulatory materials do not necessarily stimulate collagen through identical mechanisms.
For example, the CaHA narrative review discusses experimental evidence suggesting that PLLA-induced neocollagenesis is much more dependent on macrophage participation, whereas CaHA can stimulate fibroblast activity through direct microsphere–fibroblast mechanotransduction.
The same review also presents comparative experimental data showing differences in inflammatory-cell infiltration and pro-inflammatory cytokine release between CaHA and PLLA. In experiments involving M1 macrophages, CaHA was associated with lower pro-inflammatory cytokine release than PLLA.
That does not mean PLLA is inherently a bad treatment.
It has established applications and can produce clinically useful outcomes in appropriately selected patients.
It means the biology is different.
And when I have a choice between mechanisms, I personally prefer one that appears capable of stimulating extracellular-matrix regeneration without relying as heavily on a sustained inflammatory foreign-body response.
That is a philosophical choice as much as a product choice.
This is another particularly interesting part of the CaHA story.
Macrophages are still involved. CaHA is an implanted material, and the immune system participates in its eventual clearance.
But the review describes long-term CaHA degradation as involving macrophage-mediated phagocytosis and proposes that polarization towards M2-type macrophages during degradation may further support the regenerative response.
So the biological story is more nuanced than:
foreign material → inflammation → collagen.
Instead, the proposed picture looks more like:
CaHA scaffold → fibroblast mechanotransduction → extracellular-matrix production → gradual macrophage-mediated clearance, with a repair/remodelling-associated immune environment.
That is a very different regenerative philosophy.
My goal is not simply to make the skin produce more collagen. My goal is to encourage healthier tissue architecture and function.
One of your attached papers calls this the “Goldilocks zone” of regeneration.
The idea is that the regenerative stimulus should be just right.
Too little stimulation may achieve very little. But an overly inflammatory response may favour tissue replacement rather than broad restoration of normal tissue architecture.
A regenerative scaffold, the authors propose, should ideally encourage a broader restoration of tissue rather than narrowly stimulating a single component.
And CaHA is particularly interesting here because studies have reported effects beyond collagen.
There is evidence for increased elastin.
There is evidence for angiogenesis.
There is evidence for proteoglycan production—important molecules within the extracellular matrix that contribute to hydration and tissue organisation.
One study cited in the regenerative-aesthetics review reported a 76% increase in proteoglycans at six months following CaHA treatment.
That is much closer to what I mean when I talk about regenerative aesthetics.
Not forcing the body to manufacture one thing.
Trying to create conditions in which ageing tissue behaves more like healthy tissue.
There is another nuance I think patients—and even doctors—should understand.
The active ingredient alone does not tell us everything about a product.
Particle size matters.
Particle uniformity matters.
Surface morphology matters.
The carrier gel matters.
These characteristics can influence how cells and the immune system interact with an injectable material.
The CaHA review discusses how smaller or irregular particles may be more readily phagocytosed and potentially provoke greater inflammatory activity, whereas particle homogeneity, roundness and smoothness can influence immune recruitment.
It also reviews laboratory comparisons showing morphological differences between different CaHA-containing formulations. In those experiments, the CaHA-R microspheres were relatively smooth and uniform, while other tested CaHA formulations demonstrated differences in particle morphology; their short-term collagen-expression profiles also differed.
So I would be cautious about assuming:
“CaHA is CaHA.”
Formulation matters.
Manufacturing matters.
And the evidence supporting one formulation should not automatically be extrapolated to every product that happens to contain the same ingredient.
The more I study ageing biology, the less interested I become in creating inflammation simply for the sake of demonstrating a response.
Ageing tissue already exists within a complicated environment involving cellular senescence, oxidative stress, altered extracellular matrix, declining regenerative capacity, and chronic inflammatory signalling.
That doesn’t mean we should eliminate inflammation. We couldn’t—and shouldn’t.
It means I want to be thoughtful about the biological signal I introduce.
If my aim is regeneration, I increasingly want to ask:
Can we restore function rather than simply provoke repair?
Can we stimulate fibroblasts without depending predominantly on chronic inflammation?
Can we improve multiple components of the extracellular matrix rather than measuring success only by how much collagen appears?
And can we do enough to stimulate the tissue—without doing more than necessary?
These are the questions that increasingly guide the way I practise aesthetic medicine.
There are many collagen stimulators available today, and I don’t believe medicine requires every doctor to choose the same one.
My preference for CaHA comes from its biology.
I like that its proposed regenerative effect includes direct fibroblast mechanotransduction.
I like that the evidence extends beyond collagen to elastin, proteoglycans, and vascular changes.
I like that it can function as a regenerative scaffold.
And I am particularly interested in evidence suggesting that meaningful extracellular matrix regeneration can occur with comparatively limited chronic inflammatory recruitment, rather than requiring inflammation to be the dominant mechanism.
None of this means that CaHA is appropriate for everyone, every area, or every aesthetic objective.
And it certainly doesn’t mean that “more collagen” should become another aesthetic trend.
For me, the objective is much simpler:
I don’t want to irritate ageing tissue into making as much collagen as possible. I want to give it the right signals, in the right place, to help it rebuild better.
That is why, for now, CaHA remains the collagen stimulator I choose to work with at VIDASKIN.
Founded in 2015, Dr Vicki has grown with the clinic, to become one of the leading aesthetic clinicians in Singapore. She is an appointed key opinion leader and trains other aesthetic doctors on how to best use prestigious brands and treatments.
