Calcium hydroxyapatite
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Calcium hydroxylapatite, abbreviated as CaHA, is a biocompatible and biodegradable material used in aesthetic medicine as a filler and tissue biostimulator. Injectable formulations contain synthetic CaHA microspheres suspended in a gel carrier, most commonly based on carboxymethylcellulose. After administration, they provide temporary tissue support and subsequently initiate controlled remodeling of the skin's extracellular matrix. Depending on the concentration, degree of dilution, depth of injection, and the treated area, calcium hydroxylapatite can be used to model facial contours, restore volume loss, or improve skin firmness and quality. The final result also depends on the patient's anatomy, age, metabolism, and baseline tissue condition.
Calcium hydroxyapatite - what is it
Calcium hydroxyapatite is an inorganic compound with the chemical formula Ca₁₀(PO₄)₆(OH)₂. Natural hydroxyapatite is the main mineral component of bones and teeth, whereas its synthetic, highly purified form is used in medical preparations. However, chemical similarity does not mean that the material injected into the skin turns into bone. In soft tissues, CaHA microspheres form a temporary matrix around which connective tissue remodeling occurs, and are then gradually degraded.
The preparation usually has a biphasic structure:
- calcium hydroxyapatite microspheres are responsible for the biostimulating effect;
- a gel carrier facilitates the administration of the product and provides immediate, but temporary tissue support;
- selected products may contain lidocaine, which is a local anesthetic.
Undiluted or slightly diluted CaHA has volumetric properties and can be used in deeper layers to restore support and contour. The diluted or hyperdiluted form has less volume-enhancing potential, which is why it is primarily used for extensive biostimulation of the face and body skin. The choice of the preparation's form is not arbitrary. It should result from a clinical examination, skin thickness, the location of vascular structures, and the intended effect.
CaHA is not a permanent material. The carrier gel undergoes resorption earlier, while the microspheres are gradually degraded into calcium and phosphate ions, which are metabolized through the body's natural pathways. Routine allergy testing is not required, but this does not mean a complete absence of risk associated with the injection.
Calcium hydroxyapatite - how it works on the skin
The action of calcium hydroxylapatite is biphasic. Immediately after administration, the gel carrier and the rheological properties of the product provide mechanical tissue support. This can improve the projection of the treated area, the jawline contour, or the depth of a skin fold. However, part of the initial change also results from post-treatment swelling; therefore, the effect should not be evaluated solely immediately after the injection.
The second phase is biological in nature. CaHA microspheres interact with connective tissue cells and trigger a limited, controlled repair response. Histological and immunohistochemical studies, as well as a systematic review, indicate that the following may occur around the material:
- activation and proliferation of fibroblasts;
- increased collagen synthesis, especially types I and III;
- formation and reorganization of elastin fibers;
- increased production of proteoglycans, which are water-binding components of the extracellular matrix;
- improvement in the organization and mechanical properties of connective tissue;
- neovascularization, that is, the formation of small vessels supporting the metabolism of the remodeled tissue.
Consequently, the skin can gradually gain greater density, elasticity, and mechanical resistance. Clinically, improvements in tension, reduction of laxity, and smoothing of fine irregularities are observed. However, CaHA does not act like a moisturizing cosmetic and does not directly increase the water content of the skin in the same way as hyaluronic acid. The improvement in appearance results primarily from structural remodeling.
The strength of evidence is not the same for all applications. The best documented are the correction of selected facial volume deficits and the backs of the hands. Data regarding diluted CaHA applied to the neck, décolletage, arms, abdomen, thighs, knees, or buttocks are promising, but some recommendations are based on observational studies and expert consensuses. A 2023 systematic review confirmed the beneficial effect of CaHA on collagen and elastin production, while also pointing out the methodological limitations of many studies.
Calcium hydroxyapatite vs. hyaluronic acid
Calcium hydroxylapatite and cross-linked hyaluronic acid are tissue fillers, but they differ in composition, dominant mechanism of action, and management options in the event of an adverse effect.
Feature | Calcium hydroxylapatite | Hyaluronic acid |
Dominant action | Tissue support and collagen biostimulation | Volume replenishment and water binding |
Onset of effect | Partially immediate, then progressive | Usually immediate |
Skin remodeling | Pronounced biostimulatory effect | Product-dependent, usually less dominant |
Typical application | Contouring deeper structures, improving skin firmness | Precise volumetry, contouring, and filling |
Reversibility | No specific enzyme to dissolve CaHA | Possibility of degradation by hyaluronidase |
Superficial application | Limited due to the risk of lumps and product visibility | Possible for appropriately selected products |
Approximate duration | Most often about 12-18 months | Usually about 6-18 months, depending on the product and area |
Hyaluronic acid is usually preferred when very precise volume correction, the ability to build up the effect gradually, or its enzymatic reversal is required. Calcium hydroxylapatite is used when the main goal is to improve support, contour, and skin quality without intensely increasing its hydration. Diluted CaHA can act almost exclusively in a biostimulatory manner.
In a randomized study concerning nasolabial folds, CaHA provided longer-lasting correction than the hyaluronic acid products analyzed at that time, but the results of that study should not be automatically extrapolated to all modern products or anatomical areas [2]. Hybrid products combining HA and CaHA are also available. They are intended to provide immediate volumetry with subsequent biostimulation; however, they constitute a separate product category and are not a simple mixture prepared manually during the procedure.
A significant difference concerns the management of complications. Hyaluronidase breaks down hyaluronic acid, but does not dissolve CaHA microspheres. For this reason, patient qualification, selection of the injection plane, and knowledge of vascular anatomy are of particular importance when using calcium hydroxylapatite.
Calcium hydroxyapatite - how long does the effect last
The result of the procedure does not have a single, uniform duration for all patients. The effect of mechanical support is visible early on, whereas collagen remodeling develops over subsequent weeks and months. In most clinical trials, improvement was observed for approximately 12 months, and in some publications and clinical practice for 12-18 months. Some results may remain noticeable longer, however, a specific duration of the effect should not be guaranteed.
Longevity is primarily influenced by:
- the amount, properties, and degree of dilution of the product;
- the depth and technique of administration;
- the anatomical area and its mobility;
- the baseline degree of laxity or volume loss;
- age, metabolism, and the tissues' capacity to synthesize collagen;
- smoking, UV radiation, and general health status;
- the number of sessions and the intervals between them;
- concurrent performance of other procedures affecting tissue remodeling.
In a randomized study of the backs of the hands, clinical improvement was generally maintained for 12 months. Reviews concerning facial applications most frequently indicate a range of about 12-18 months, but emphasize variations in protocols and evidence quality. Follow-up evaluation should take into account both visual appearance and tissue palpation. The decision regarding subsequent administration should not be based solely on the passage of a specific amount of time.
Calcium hydroxyapatite treatments
Ambasada Urody offers treatments performed with Radiesse and Crystalys preparations. Radiesse is a CaHA preparation with volumizing and biostimulating properties. Crystalys also contains calcium hydroxyapatite microspheres in a gel carrier and is intended for modeling deeper tissues and stimulating collagen remodeling. The products should not be treated as automatically interchangeable, as they may differ in composition, rheological parameters, and manufacturer indications.
Available applications include:
- face: cheeks, cheekbones, nasolabial folds, marionette lines, chin area, and jawline;
- full-face therapy: combining the restoration of mid- and lower-face support with contour improvement;
- neck and décolletage: the use of diluted or hyperdiluted preparation to improve skin tension and quality;
- hands: replenishing volume loss on the back of the hands, reducing the visibility of tendons and vessels, and improving skin quality;
- bust and upper breast area: improving skin tension and the appearance of the décolletage, without replacing a surgical breast lift or implant;
- arms: treatment of lax skin, especially on their medial surface;
- abdomen: improving skin quality after pregnancy, aging, or weight loss;
- thighs and knee area: skin redensification and firming;
- buttocks: improving the quality, tension, and subtle modeling of superficial tissues.
Diluted CaHA is not intended for significant breast or buttock enlargement. It also does not remove excess skin and does not replace surgery in cases of advanced laxity. The scope of application must remain consistent with the instructions of the specific product.
Typical short-term side effects include pain, tenderness, swelling, redness, bruising, and transient unevenness. Papules, nodules, induration, chronic inflammation, infection, or asymmetry are also possible. A rare but most serious complication of fillers is accidental intravascular injection, which can lead to ischemia and skin necrosis, visual impairment, and, in exceptional cases, loss of vision.
The most important contraindications or reasons for postponing the procedure include active infection and inflammation at the injection site, pregnancy or breastfeeding due to a lack of sufficient data, bleeding disorders, uncompensated systemic diseases, hypersensitivity to product ingredients, and unrealistic expectations. Qualification should include a medical history regarding autoimmune diseases, a tendency toward abnormal scarring, medications taken, previous fillers, and past procedures. The injection should be performed by a physician knowledgeable in the anatomy of the given area as well as procedures for recognizing and treating complications.
