Kybella contains a synthetic form of deoxycholic acid, a bile acid your body already produces naturally to break down dietary fat. Each 2 mL vial holds 20 mg of this active ingredient at a concentration of 10 mg/mL, along with a short list of inactive ingredients that keep the solution stable and sterile. The FDA approved Kybella in 2015 specifically for reducing moderate to severe fat beneath the chin.
The Active Ingredient: Synthetic Deoxycholic Acid
Deoxycholic acid is classified as a secondary bile acid. Your liver and gut bacteria produce it as part of normal digestion, where it helps dissolve and absorb fats from food. The version in Kybella is made synthetically in a lab rather than derived from animal sources, but FDA testing confirmed that the synthetic and animal-derived forms have identical cell-destroying potential.
When injected into fat tissue beneath the chin, deoxycholic acid physically ruptures the outer membrane of fat cells, destroying them permanently. This process is called cytolysis. Because the treatment dose doesn’t meaningfully increase your body’s overall lifetime exposure to deoxycholic acid, the FDA waived the requirement for long-term cancer risk studies.
Inactive Ingredients
Beyond the active ingredient, each vial of Kybella contains:
- Benzyl alcohol (18 mg): a preservative that prevents bacterial contamination
- Dibasic sodium phosphate (2.84 mg): a buffering agent that keeps the solution at a stable pH
- Sodium chloride (8.76 mg): salt, used to match the solution’s concentration to your body’s fluids
- Sodium hydroxide (2.86 mg): a pH adjuster
- Water for injection: the sterile base of the solution
Small amounts of hydrochloric acid and additional sodium hydroxide are added as needed to bring the final formulation to a pH of 8.3, which is slightly alkaline. The finished product is a clear, colorless, sterile solution.
How It Works Under the Skin
Kybella is injected directly into the layer of fat beneath the chin, an area called the submental region. The deoxycholic acid contacts fat cells and breaks apart their outer membranes. Once a fat cell’s membrane is destroyed, the cell can no longer store fat and is cleared away by your body’s normal metabolic processes over the following weeks. Those cells do not regenerate, which is why results are considered permanent as long as your weight remains stable.
This cell-destroying action is not selective to fat alone, which is why precise injection placement matters. If the solution reaches the wrong tissue, it can damage nearby structures. The FDA label warns that injections placed too shallow (into the skin itself rather than the fat layer) can cause ulceration and tissue death at the injection site.
What Kybella Is Approved to Treat
Kybella is approved only for reducing fullness beneath the chin in adults. The FDA label explicitly states that its safety and effectiveness for treating fat in other body areas has not been established and is not recommended. Despite this, some providers use it off-label in areas like the jowls or bra fat, but those uses fall outside the studied and approved indication.
Risks Tied to the Formula
Because deoxycholic acid destroys any cell membrane it contacts, the main risks center on what happens if the injection reaches tissue other than fat. The most notable concern is injury to the marginal mandibular nerve, a branch of the facial nerve that runs along the jawline. Damage to this nerve showed up in clinical trials as an asymmetric smile or weakness in the facial muscles. This side effect is typically temporary but is the reason injection placement requires precise anatomical knowledge.
The FDA label also warns providers to keep injections at least 1 to 1.5 cm away from salivary glands, lymph nodes, and muscles. Injecting into or near a blood vessel can cause vascular injury. Cases of injection site infection, including some requiring IV antibiotics or drainage, have been reported after treatment.
Common, expected side effects like swelling, bruising, numbness, and firmness beneath the chin are a direct result of the cell-destruction process and the body’s inflammatory response to clearing out damaged tissue. These typically resolve within a few weeks after each session.