Injectable fillers are medical implants used to restore lost volume, smooth wrinkles, and reshape facial contours. They’re FDA-approved for use in adults over 21 to treat specific areas including the cheeks, lips, chin, nasolabial folds (the lines running from your nose to the corners of your mouth), and the backs of the hands. But their purposes extend well beyond cosmetic enhancement into medical territory, including correcting facial asymmetry and treating disease-related fat loss.
How Fillers Work in the Body
The most common injectable fillers are made from hyaluronic acid, a substance your body already produces naturally. Hyaluronic acid carries a strong negative charge that attracts water molecules. When injected beneath the skin, it pulls in surrounding moisture, swelling to create immediate volume and structural support in the treated area.
What happens as the filler breaks down is particularly interesting. As your body gradually degrades the hyaluronic acid gel, water replaces the dissolving material and occupies the same space. This process, called isovolumetric degradation, is why results don’t vanish overnight. Your appearance changes gradually over months rather than dropping off suddenly.
Other filler types work through a completely different mechanism. Products made from poly-L-lactic acid (PLLA) or calcium hydroxyapatite (CaHA) act as biostimulators. Rather than simply filling space, they trigger your skin’s own cells to produce new collagen and connective tissue. The filler material itself eventually dissolves, but the collagen it helped generate remains, providing longer-lasting structural improvement.
Cosmetic Uses: Volume, Contour, and Definition
The cosmetic applications of fillers fall into several distinct categories, each serving a different structural goal.
Replacing lost facial volume. As you age, the fat pads beneath your skin shrink and shift downward. This is especially noticeable in the midface, where deep fat pads sit beneath the cheek muscles. When these deflate, your cheeks flatten and the skin above your nasolabial folds sags forward, deepening those lines. Fillers injected into these deep fat pads restore the internal scaffolding that keeps your midface lifted. Research on midface anatomy has shown that targeting these deep structures specifically, rather than filling superficially, produces longer-lasting results and can even stimulate the expansion of the fat tissue’s own stem cells.
Smoothing wrinkles and fine lines. Fillers address both deep folds like nasolabial lines and finer wrinkles like the small creases around the mouth (perioral lines). Superficial placements smooth the skin’s surface, while deeper injections address the structural collapse underneath that causes the fold in the first place.
Enhancing and defining the lips. Lip fillers serve three separate purposes that can be combined in a single treatment. They can increase overall fullness for naturally thin lips or lips that have lost volume with age. They can sharpen the vermilion border, the outline of your lips that tends to blur over time, which also helps prevent lipstick from feathering. And they add hydration, since hyaluronic acid’s water-attracting properties give lips a softer, more supple texture.
Reshaping the chin and jawline. Fillers placed along the chin and jaw can improve facial proportions, add projection to a recessed chin, or create a more defined jawline without surgery.
Rejuvenating the hands. The backs of the hands lose fat with age, leaving tendons and veins prominently visible. Filler injections in this area restore a smoother, fuller appearance. This is one of the FDA’s specifically approved uses.
Medical and Reconstructive Purposes
Not all filler use is elective. Several products carry FDA approval for treating HIV-associated facial lipoatrophy, a condition where antiretroviral medications cause significant fat loss in the cheeks, temples, and eye sockets. This visible wasting can be socially stigmatizing and psychologically damaging. Filler injections restore facial volume in these patients, and both PLLA and CaHA fillers are specifically approved for this purpose. Hyaluronic acid fillers are also used and offer the added advantage of being reversible if adjustments are needed.
Fillers also serve reconstructive purposes outside of HIV treatment. They can correct facial asymmetry from trauma, smooth depressed acne scars (non-absorbable permanent fillers are approved specifically for cheek acne scars), and address contour deficiencies from injury or congenital conditions. In asymmetry cases, different amounts of filler are injected on each side to achieve a balanced result.
How Long Results Last
Duration depends on the product type, where it’s placed, and how quickly your body metabolizes it. Hyaluronic acid fillers placed in areas with significant movement, like the lips, tend to break down faster and typically last 6 to 12 months. Deeper injections in areas with less movement, like the cheeks, can last up to 12 months, with some newer products lasting as long as two years. Biostimulatory fillers like PLLA often produce results that outlast the product itself, since the collagen they generate remains after the filler material has dissolved.
The Safety Advantage of Reversibility
One of the key reasons hyaluronic acid fillers dominate the market is that they can be dissolved. An enzyme called hyaluronidase, which your body produces naturally, breaks down hyaluronic acid on contact. If a filler produces an unwanted result, causes a nodule, or in rare emergency situations blocks blood flow to tissue, a provider can inject hyaluronidase to reverse the effect.
A randomized clinical trial published in JAMA Dermatology confirmed that even low doses of this enzyme effectively dissolve filler nodules, with higher doses producing faster resolution. At both 4-week and 4-month follow-ups, treated areas showed significantly more filler dissolution compared to saline controls. This reversibility acts as a built-in safety net that other filler types, including PLLA, CaHA, and permanent fillers, do not offer.
That distinction matters when choosing a product. Permanent fillers are approved only for nasolabial folds and cheek acne scars, precisely because they cannot be removed if problems develop. For most cosmetic purposes, temporary fillers with a clear exit strategy carry a more favorable risk profile.