Most dermal fillers are made from a sugar molecule your body already produces, suspended in a gel with a small amount of numbing agent and saline. The exact ingredients depend on which type of filler is used, but there are four main categories approved for cosmetic injection in the United States: hyaluronic acid fillers, calcium hydroxylapatite fillers, poly-L-lactic acid fillers, and one permanent filler made with tiny plastic microspheres.
Hyaluronic Acid: The Most Common Ingredient
The vast majority of fillers on the market, including the Juvederm and Restylane product lines, are built around hyaluronic acid. This is a sugar-based molecule that your body naturally produces in skin, joints, and connective tissue, where it holds onto water and keeps things cushioned. In filler form, hyaluronic acid is manufactured by bacteria in a lab rather than harvested from animals. The molecule itself is identical regardless of its source.
Raw hyaluronic acid would dissolve in your body within a day or two. To make it last, manufacturers chemically link the molecules together using a cross-linking agent called BDDE. This creates a stable, three-dimensional gel network that resists your body’s natural enzymes for months instead of hours. The FDA requires that the final product contain less than 2 parts per million of unreacted BDDE, a trace amount considered safe for injection.
After cross-linking, the gel goes through a purification process using sodium chloride solution and phosphate buffer. These steps adjust the pH to match your tissue, control the salt balance so the filler doesn’t cause irritation, and flush out any leftover cross-linking chemicals. The finished syringe contains the cross-linked hyaluronic acid gel, buffered saline, and in most modern formulations, about 0.3% lidocaine (a local anesthetic) to reduce pain during injection. That’s it. The effects typically last 6 to 12 months before the body fully breaks the gel down.
How Your Body Breaks Down HA Fillers
Your body produces an enzyme called hyaluronidase that naturally chews through hyaluronic acid by snipping the chemical bonds holding the sugar chains together. Cross-linking slows this process dramatically, but it doesn’t stop it. Over months, the enzyme gradually dismantles the gel into simple sugars and water, which your body absorbs and clears normally.
This same enzyme can be injected on purpose if a filler needs to be dissolved, whether for a complication or simply to reverse an unwanted result. How quickly it works depends on the filler’s concentration, the density of its cross-links, and the amount of enzyme used. One practical advantage of hyaluronic acid fillers over every other type is this built-in reversibility.
Calcium Hydroxylapatite Fillers
The brand Radiesse uses a completely different material. It contains 30% synthetic calcium hydroxylapatite microspheres, tiny smooth particles 25 to 45 micrometers in diameter, suspended in a 70% water-based gel made from carboxymethylcellulose (a plant-derived thickener commonly used in food products). The calcium hydroxylapatite itself is chemically identical to the mineral component of your bones and teeth.
This filler works in two phases. The gel provides immediate volume, then gradually absorbs over a few weeks. The microspheres remain longer, acting as a scaffold that stimulates your body to produce new collagen around them. Over time, the microspheres themselves slowly break down into calcium and phosphate ions, which your body processes normally. Results last approximately 18 months. Unlike hyaluronic acid fillers, there is no enzyme that can dissolve Radiesse on command.
Poly-L-Lactic Acid Fillers
Sculptra takes yet another approach. Each vial contains a powder made of three ingredients: poly-L-lactic acid (a synthetic polymer from the same family as dissolvable stitches), carboxymethylcellulose, and mannitol (a sugar alcohol used as a stabilizer). Before injection, the powder is mixed with sterile water to create a suspension, and lidocaine can be added for comfort.
Poly-L-lactic acid doesn’t add volume the way hyaluronic acid does. Instead, it triggers a gradual collagen-building response in the tissue. The material itself is slowly absorbed over weeks, but the collagen your body produces in response can keep results visible for up to two years. This makes Sculptra less of a traditional filler and more of a collagen stimulator, typically used for broader volume loss rather than precise shaping.
The One Permanent Filler
Bellafill is the only FDA-approved filler designed to be permanent. Each syringe is 20% polymethylmethacrylate (PMMA) microspheres and 80% bovine collagen solution. Breaking that carrier solution down further: it’s 92.6% buffered water, 3.5% collagen derived from cows, 2.7% phosphate buffer, 0.9% sodium chloride, and 0.3% lidocaine. The PMMA microspheres are 30 to 50 micrometers in diameter.
The collagen gel provides immediate volume and gradually absorbs over one to three months. The PMMA microspheres, however, are not biodegradable. Your body encapsulates them in new collagen tissue, creating a permanent structural support. Because of the bovine collagen, a skin test is recommended before the first treatment to check for allergic reactions. The permanence is both the appeal and the risk: if you don’t like the result, or if a problem develops years later, removal is far more complicated than with any temporary filler.
What All Fillers Have in Common
Regardless of the active ingredient, most fillers share a few supporting components. A buffered saline solution (water, sodium chloride, and phosphate buffer) keeps the pH close to your body’s natural level, around 7.0 to 7.4, so the injection doesn’t sting or damage tissue. Lidocaine at roughly 0.3% concentration is now standard in most pre-mixed syringes to numb the area during injection. And every approved filler is sterile, packaged in single-use syringes.
The differences that matter most between fillers come down to the main ingredient: how long it lasts, whether it can be reversed, and whether it adds volume directly or stimulates your body to build its own. Hyaluronic acid fillers give the shortest results but offer the most control and reversibility. Calcium hydroxylapatite and poly-L-lactic acid last longer but can’t be dissolved if something goes wrong. PMMA is permanent, for better or worse.