Problems after Fat-Dissolving Injections and Mesotherapy: Swelling, Hardness, Infection — When Is It an Emergency?

What are fat-dissolving injections, and how do they differ from mesotherapy?

Fat-dissolving injections (injection lipolysis) involve injecting substances that break down the membrane of fat cells directly into the fat tissue under the skin. The substances used most often are deoxycholic acid and phosphatidylcholine; in some treatments, vitamins, plant extracts and other substances are also added. These mixtures are also commonly known as fat-burning cocktails or mesotherapy.

Classic mesotherapy, by contrast, is based on injecting very small amounts of different substances into the skin; for details, see our article “Mesotherapy”. In some countries there is a product whose active substance is deoxycholic acid that has been approved as a medicine only for fat under the chin. Apart from this, the safety and effectiveness of most mixtures sold for dissolving fat have not been assessed by medicines regulators.

What is normal after fat-dissolving injections?

As these substances break down fat cells, they create a controlled inflammation in the area. This is why marked swelling, pain, warmth, bruising and numbness lasting a few days are common. With treatments under the chin, the swelling can be striking in the first days.

Mild hardness that can be felt in the treated area for weeks is also expected and usually softens gradually. For general information about bruising and swelling, see our article “Bruising and Swelling”.

How long do swelling, hardness and nodules last?

Swelling is usually most noticeable in the first days and gradually goes down. Hardness, on the other hand, can be felt for weeks while the fat tissue heals. If this hardness is not painful, gradually getting smaller and the skin over it is a normal colour, it is usually part of the expected course.

In a warning published in 2026, the U.S. Food and Drug Administration (FDA) announced that, after approved deoxycholic acid injection, nodules and masses had been reported in some people that did not go away for months and could require medical intervention. Show nodules that are growing, painful, red or not getting smaller after several months to a physician.

How can you recognise an infection after fat-dissolving injections?

Infection can appear in the days after the treatment or weeks later. With early infection there is increasing redness, warmth, pain, pus-like discharge and fever. With infections that start later, swellings stand out at the injection points that appear over weeks, are red-purple, painful, sometimes discharging and grow slowly.

A large proportion of these late infections are caused by germs called atypical mycobacteria, which do not respond to ordinary antibiotics. In an outbreak in France affecting 16 people after mesotherapy by the same practitioner, recovery took about six months on average; patients needed surgical drainage and long-term medication. These infections are mostly linked to non-sterile products, equipment or settings. For general information, see our article “Infection after Aesthetic Treatments”.

Why do darkening of the skin or open wounds occur?

When the fat-dissolving substance is injected too close to the skin instead of into the fat tissue beneath it, or when it affects a blood vessel, darkening of the skin, a purplish net-like discolouration, crusting and a wound (ulcer) can develop. This may indicate that the skin tissue has been damaged and should be assessed without delay.

Early intervention can support healing of the tissue and reduce the risk of scarring. Do not apply creams to the area on your own, do not apply heat, and do not pick off crusts.

Why can the smile become uneven after treatment under the chin?

A thin nerve branch that moves the lower lip runs along the lower edge of the jawbone. If this nerve is affected during injections for fat under the chin, one side of the lower lip cannot move down when you smile, and the smile looks uneven. This nerve effect is listed as a known risk in the prescribing information of the approved deoxycholic acid product.

In large clinical trials, this nerve effect was reported to be mostly mild and temporary and to resolve without lasting problems. Even so, any newly appearing loss of movement should be reported to a physician the same day. Difficulty swallowing, marked swelling of the neck and hair loss in the beard area are other problems reported after treatments in this area.

Can dents and unevenness appear on the surface?

When fat-dissolving substances affect the fat tissue in an uncontrolled way or are distributed unevenly, dents, rippling and a difference between the two sides can appear on the surface. Too much fat loss can give an aged or hollow look, especially on the face and along the jawline. Such irregularities sometimes decrease over time; if they do not, the physician will consider suitable correction options. It is difficult to judge the final appearance before the swelling and hardness have fully gone, so you generally need to wait a few months before deciding on a correction. Having another fat-dissolving treatment in the same area during this time can make the unevenness worse.

Why are fat-dissolving cocktails of unknown origin risky?

The FDA has announced that permanent scarring, serious infections, skin deformities, cysts and deep painful nodules have been reported after unapproved fat-dissolving injections sold online or given by unlicensed people. The contents, purity and sterility of these products are unknown, and the correct amount and depth are often not used.

Do not inject a product whose contents are not disclosed, that is unlabelled or that was bought online into yourself or anyone else. For details, see our article “Counterfeit Products and Unlicensed Treatments”.

If there is a problem, what should you do at home, and what should you avoid?

1. Note the symptoms and when they started; take photos at regular intervals in the same lighting.
2. Find out the name and contents of the product used and the date of treatment; keep any packaging or records you have.
3. If you have any of the warning signs, call the physician who performed the procedure the same day.
4. If you cannot reach your physician and you have a discharging swelling, a wound, fever, difficulty swallowing or loss of facial movement, go to an emergency department and say which product was used.

• Do not squeeze swellings and nodules or prick them with a needle.
• Do not massage or apply heat to the area unless the physician recommends it.
• Do not use antibiotics or steroid medicines you have at home on your own; with atypical infections, the wrong treatment can delay the diagnosis.
• Do not have new injections in the same area; the cause of the problem must be understood first.
• Do not wait for weeks thinking it will go away on its own; with late infections, early diagnosis is important.

What are the treatment options? What can the physician do?

The physician will first assess whether the problem is the expected inflammatory reaction or an infection, tissue damage, a nerve effect or unevenness. If needed, imaging such as ultrasound may be used. With late-onset, discharging swellings, it is important to take a sample and carry out a special culture to identify the right germ.

Treatment of atypical mycobacterial infections often requires several medicines taken together for months and sometimes surgical drainage. Wound care may be discussed for wounds and tissue damage, follow-up for nerve effects, and correction options once healing is complete for unevenness that does not go away. For the general process, see our article “What Should You Do If a Complication Occurs after an Aesthetic Treatment?”.

What can be done to reduce the risk?

• Be aware that fat-dissolving injections are not a weight-loss method; first discuss diet, exercise and, where appropriate, other methods with your physician.
• Have the treatment only after an examination by a physician, in a licensed healthcare facility where sterile conditions are ensured.
• Ask for the name, contents and licensing status of the product to be used; ask for it to be opened in front of you from its sealed, original packaging.
• Do not accept mixtures whose contents are not disclosed on the grounds of being a special formula, products sold online or treatments carried out at home.
• Mention the medicines you take, any tendency to bleed, previous treatments in the area and any existing problems with swallowing or facial movement.
• When choosing a physician and clinic, use our article “A 10-Point Safety Checklist for Choosing a Clinic and Physician for Medical Aesthetics”.

Limits of the evidence: the safety and effectiveness of fat-dissolving mixtures other than the approved deoxycholic acid product have largely not been studied; serious problems are mostly known from case reports and official warnings. For this reason, you cannot be given a personal risk figure. This page is for general information and does not replace an examination.