A filler injection is a cosmetic procedure where a gel-like substance is injected beneath the skin to restore lost volume, smooth wrinkles, or enhance facial features like lips and cheeks. The results are typically visible immediately, and the procedure itself takes anywhere from 15 minutes to an hour depending on the treatment area. Fillers are one of the most common nonsurgical cosmetic treatments performed today, with over 20 commercially available products on the market.
What Fillers Are Made Of
Most fillers used today fall into a few material categories, each with different properties and uses.
The most popular type is hyaluronic acid, a substance your body already produces naturally as part of the structural matrix of your skin. For cosmetic use, it’s manufactured as a gel from bacteria-derived sources, then chemically reinforced (crosslinked) so it holds its shape longer after injection. Hyaluronic acid fillers have been FDA-approved since 2003 and come in more than 20 formulations, each with a slightly different thickness and texture suited to different areas of the face.
Calcium hydroxylapatite fillers, approved since 2006, use tiny microspheres made of the same calcium and phosphate minerals found in human bone, suspended in a gel carrier. These tend to be thicker and are often used for deeper lines or areas that need more structural support, like the cheeks and jawline.
A third category, poly-L-lactic acid, works differently from the others. Rather than simply filling space, it triggers your body’s own collagen production over several months. The initial volume from the injection fades within a week as the liquid carrier is absorbed, and the real results develop gradually. Fibroblasts (the cells that build collagen) hit their peak activity around six months after injection, producing collagen that can last two years or longer.
How Fillers Work in the Skin
Traditional fillers physically occupy space beneath the skin, providing immediate lift and structure to areas affected by volume loss or wrinkles. Think of them as a cushion placed under the skin’s surface. When injected into the cheeks, for instance, the gel pushes the overlying skin upward, restoring the fullness that naturally diminishes with age. In the lips, the filler expands the tissue from within, creating a plumper appearance.
This is fundamentally different from how neurotoxin injections (like Botox) work. Neurotoxins are injected into facial muscles to temporarily weaken them, reducing wrinkles caused by repeated movement, like crow’s feet and forehead lines. Fillers are injected into the skin itself, not the muscle, and address wrinkles caused by volume loss rather than muscle activity. Many people get both treatments at the same time for different areas of the face.
Where Fillers Can Be Used
The FDA has approved fillers for adults 22 and older in several specific areas. These include nasolabial folds (the lines running from the sides of your nose to the corners of your mouth), small lines around the mouth, lips, cheeks, chin, and the back of the hands. Fillers are also approved for correcting acne scars and restoring facial volume lost due to certain medical conditions, including HIV-related fat loss.
Off-label use is also common. Many practitioners inject fillers into the under-eye area (tear troughs), temples, jawline, and nose for nonsurgical reshaping. These uses aren’t specifically FDA-cleared, but they’re widely practiced in cosmetic medicine.
How Long Results Last
Hyaluronic acid fillers have traditionally been described as lasting 3 to 12 months, depending on the product, the treatment area, and your individual metabolism. However, recent imaging research has challenged that timeline significantly. A review of 33 patients who underwent MRI scans found that hyaluronic acid filler remained detectable in the mid-face for at least two years in every single patient. Some patients still had visible filler 5, 8, and even 15 years after injection. This doesn’t necessarily mean the cosmetic effect lasts that long, since the filler can migrate or change shape over time, but the material itself persists far longer than previously thought.
Poly-L-lactic acid fillers work on a different timeline entirely. The initial injection volume disappears within a week, and the collagen-building process unfolds over months. New collagen fibers start appearing around 16 weeks, with the most significant volume developing at the six-month mark. The results from that new collagen can persist for two years or more.
What to Expect Before Treatment
Preparation is straightforward but important for minimizing bruising. Stanford Medicine’s pre-treatment guidelines recommend avoiding alcohol for at least 24 hours beforehand, as it thins the blood and increases bruising risk. If you regularly take anti-inflammatory painkillers like ibuprofen or aspirin, stopping those before your appointment (with your prescriber’s approval) can also help. Retinoid skin products should be discontinued two days before and two days after treatment.
The procedure itself involves a series of small injections, often with a fine needle or blunt-tipped cannula. Most modern fillers contain a local anesthetic mixed into the gel, and practitioners typically apply a numbing cream beforehand as well. Discomfort varies by area. Lips tend to be the most sensitive, while cheeks and jawline are generally more tolerable.
Recovery and Side Effects
Swelling is the most common side effect, peaking around 24 to 72 hours after treatment. You may also notice redness, tenderness, itching, or bruising at the injection sites. The swelling begins to ease noticeably by day three or four, and most people see significant improvement by the end of the first week. Bruising can linger a bit longer. By two weeks, nearly all visible side effects have resolved and the final result becomes clear.
There’s no real downtime. Most people return to normal activities the same day, though strenuous exercise and heat exposure are typically avoided for 24 to 48 hours.
Serious Risks to Know About
The most concerning complication is vascular occlusion, where filler is accidentally injected into or compresses a blood vessel. This can cut off blood supply to the surrounding skin, potentially causing tissue death. In extremely rare cases involving blood vessels near the eyes, it can affect vision. A large-scale analysis calculated the incidence of vascular events at roughly 1 in 6,600 filler injections (about 0.015%). Warning signs include a sudden bluish, net-like discoloration of the skin, unusual blanching (whitening), or disproportionate pain during or shortly after injection.
This is one reason hyaluronic acid fillers have a built-in safety advantage over other types. An enzyme called hyaluronidase can dissolve hyaluronic acid filler rapidly when injected into the affected area. It works by breaking down the chemical bonds that hold the filler gel together, essentially reversing the treatment. No equivalent reversal agent exists for calcium hydroxylapatite or poly-L-lactic acid fillers, which is worth considering when choosing a filler type, especially for first-time patients.
Less serious but more common complications include lumps or nodules at the injection site, asymmetry, and prolonged swelling. Most of these can be managed with massage, hyaluronidase (for hyaluronic acid fillers), or simply waiting for the filler to settle.