Fat Necrosis After BBL: Causes, Signs and Treatment

In this guide17 sections

1. Key Points
2. What Is Fat Necrosis After a BBL?
3. What Is an Oil Cyst After a BBL?
4. How Common Is Fat Necrosis After a BBL?
5. What Causes Fat Necrosis After a BBL?
6. What Are the Signs of Fat Necrosis After a BBL?
7. When Does Fat Necrosis Happen After a BBL?
8. Is It Fat Necrosis, a Seroma or an Infection?
9. How Is Fat Necrosis Diagnosed?
10. Does Fat Necrosis Go Away on Its Own?
11. How to Get Rid of Fat Necrosis After a BBL
12. Will Fat Necrosis Ruin My BBL Result?
13. How to Prevent Fat Necrosis After a BBL
14. When Should You Seek Help for a Lump After a BBL?
15. Frequently Asked Questions
16. Brazilian Butt Lift in London
17. References

Fat necrosis after a BBL is the death of some of the transferred fat, which leaves firm lumps, tender areas or oil cysts in the buttocks. It is uncommon after a Brazilian butt lift in which the fat is injected only into the layer under the skin with ultrasound guidance, and most small areas of BBL fat necrosis soften over a few months without treatment. Lumps that persist or cause symptoms can be aspirated, removed with liposuction or excised.

This guide covers what fat necrosis and oil cysts are, how often they happen, their causes, how to tell them from a seroma or infection, diagnosis, treatment and when to seek help. It sits alongside our overview of BBL risks, which covers every complication of the operation, and our guide on how to prevent dents after a BBL, as dents and fat necrosis often have the same causes.

What Is Fat Necrosis After a BBL?

Fat necrosis is the medical name for fat tissue that has died. In a BBL, fat is taken from areas such as the abdomen, flanks and back by liposuction, processed and then injected into the buttocks. Unlike a skin graft or flap, the transferred fat arrives with no blood vessels of its own. It survives in the first days by soaking up oxygen and nutrients from the surrounding tissue, and then grows new blood vessels into the graft.

Fat cells are very sensitive to a lack of oxygen. A 2012 experimental study in Plastic and Reconstructive Surgery ↗ showed that most fat cells in a graft start to die on the first day, and only those within about 0.3 mm of the graft’s edge reliably survive^[1]. The researchers described an outer surviving zone, a middle zone where dead fat cells are replaced by new ones, and a central zone where everything dies. That central zone is fat necrosis.

Some loss is expected in every BBL: around 50% to 70% of transferred fat survives, and the rest is cleared quietly by the body, which is why surgeons slightly overfill. Our guide to how much fat is transferred in a BBL explains how volumes are planned. Fat necrosis is different: it is dead fat the body cannot clear quickly, so it walls off into a lump you can feel.

What Is an Oil Cyst After a BBL?

When dead fat cells break open, they release their oily contents, and the body surrounds this oil with a thin capsule to form an oil cyst. An oil cyst is a type of fat necrosis. The forms you may notice are:

• Oil cysts: smooth, round, often mobile lumps that feel rubbery or slightly squashy.
• Solid fat necrosis: a firmer, irregular knot of scarred fat tissue.
• Calcified fat necrosis: an older lump whose capsule has hardened, which is less likely to shrink on its own.
• A larger liquefied collection: rarely, a substantial area of fat fails to take and forms a collection of oil and fluid that can slowly enlarge, sometimes many months after surgery^[2].

Fat necrosis is benign. It is not cancer and does not turn into cancer.

How Common Is Fat Necrosis After a BBL?

Published rates vary widely, mainly because some studies count only lumps patients notice while others count anything seen on a scan. The best current figures are:

• Ultrasound-guided BBL: a 2025 systematic review and meta-analysis in the Aesthetic Surgery Journal ↗ pooled four studies of 6,235 patients who had ultrasound-guided gluteal fat grafting. Fat necrosis occurred in 0.09 per 100 patients, compared with 2.94 per 100 for seroma and 0.23 per 100 for infection, with no deaths or fat embolism reported^[3].
• Non-embolic complications overall: a 2026 systematic review of 18 studies and 12,032 patients found a non-embolic complication rate of 2.67%. Fat necrosis made up 14.3% of those complications and cyst formation a further 10.6%, so together they were about a quarter of the problems that were not fat embolism^[4].
• A single large series: one clinic reporting 7,000 consecutive subcutaneous-only BBLs recorded fat necrosis in 1.9% of patients, using average volumes of about 1,200 ml per buttock^[5].

Technique matters: a 2025 meta-analysis of 22,151 patients found the lowest complication rates with subcutaneous-only injection, and fewer minor complications with ultrasound guidance (2.82% compared with 3.70%)^[6]. At Centre for Surgery, fat is injected only into the subcutaneous layer above the gluteal muscle under real-time ultrasound on every BBL, as explained in our guide to ultrasound-guided BBL.

What Causes Fat Necrosis After a BBL?

All the causes of fat necrosis come back to one problem: part of the graft does not get enough blood supply in the first days and weeks. The main reasons are:

Large boluses of fat

Fat injected as a large pool, rather than in many thin threads, has a centre too far from living tissue to get oxygen; the 0.3 mm survival zone shows how thin each deposit needs to be^[1]. Volume matters too: in an imaging study of breast fat grafting, patients who developed fat necrosis had received more fat on average (158 ml compared with 105 ml)^[7]. Expansion vibration lipofilling (EVL), used at Centre for Surgery, spreads the fat in fine layers for this reason.

Poor blood supply in the recipient area

Overfilling one area raises the pressure inside the tissue and squeezes the small vessels the graft depends on. Thin or scarred tissue, such as after a previous BBL, filler injections or an injury, has fewer vessels to share. A fall or a hard knock to the buttocks can also cause fat necrosis.

Pressure on the buttocks after surgery

Sitting or lying directly on the buttocks in the first weeks compresses the new fat while it is trying to grow a blood supply. Centre for Surgery asks patients not to sit directly on the buttocks for 2 weeks, to use a BBL cushion if sitting is unavoidable and to sleep on the front or side rather than the back for 2 weeks. Have a BBL cushion ready before your operation. Our guide on when you can sit after a BBL sets out each stage.

Smoking and nicotine

Nicotine narrows small blood vessels and carbon monoxide reduces the oxygen carried in the blood, which is exactly what a new fat graft cannot afford. A 2012 meta-analysis of 140 cohort studies in Archives of Surgery ↗ found that smokers had 3.6 times the odds of tissue necrosis after surgery compared with non-smokers^[8]. Vaping and nicotine replacement still deliver nicotine, so Centre for Surgery asks patients to stop all nicotine for 4 weeks before and 4 weeks after a BBL. Our article on smoking and cosmetic surgery explains more.

Rough handling of the fat during harvesting, and untreated infection or seroma next to the graft, can also add to the amount of fat that dies.

What Are the Signs of Fat Necrosis After a BBL?

The signs of fat necrosis after a BBL usually appear between a few weeks and a few months after surgery, once the early swelling has started to settle:

• Firm lumps: one or more hard or rubbery lumps under the skin, usually where the most fat was placed.
• Tenderness: often painless, but some lumps are tender or uncomfortable to sit on.
• Skin changes: mild redness, bruise-like discolouration, dimpling or an uneven contour over the lump.
• Oily drainage: rarely, an area near the surface breaks through the skin and drains a yellow, oily fluid.

Fat necrosis itself does not usually smell. A bad smell, pus, spreading redness and heat or a high temperature suggest infection and need to be seen the same day. Darkened skin that is breaking down is skin necrosis rather than fat necrosis, and also needs urgent review.

When Does Fat Necrosis Happen After a BBL?

The fat that is going to die does so in the first days to weeks, while the graft waits for new blood vessels. Lumps often only become noticeable later:

• Weeks 1 to 4: the buttocks are swollen and firm all over, so single lumps are hard to judge. A red, hot area now is more likely to be infection, and a soft, fluid area a seroma.
• Weeks 4 to 12: as swelling settles, lumps of fat necrosis or oil cysts become easier to feel. Most are first noticed in this window.
• 3 to 12 months: small lumps often shrink and soften, and persistent ones are assessed.
• A year or more: a lump may be noticed for the first time, or an old oil cyst may slowly enlarge^[2].

Normal firmness after a BBL can feel lumpy too, and it softens as part of “fluffing”, usually around 6 to 8 weeks, as our guide to when fluffing happens after a BBL explains.

Is It Fat Necrosis, a Seroma or an Infection?

Hard lumps after a BBL have several possible causes, and the treatment depends on which one you have:

• Normal swelling: both buttocks feel firm and full all over, with no single distinct lump. It peaks at 3 to 5 days and settles over weeks.
• Seroma: a collection of clear or straw-coloured fluid, most often in the liposuction areas such as the lower back and flanks. It feels soft and wobbly and usually appears in the first 1 to 3 weeks. Seroma is far more common than fat necrosis, at 2.94 per 100 in the ultrasound-guided meta-analysis^[3], and is drained with a needle.
• Infection: spreading redness, heat, worsening pain, discharge or a bad smell, often with fever, usually in the first 1 to 2 weeks. It needs prompt antibiotics and sometimes drainage.
• Fat necrosis or oil cyst: a distinct firm or rubbery lump, usually without fever, noticed from a few weeks after surgery and changing slowly.

These can overlap: a seroma or infection can damage nearby fat, and fat necrosis can become infected. You cannot reliably tell them apart at home, so contact your surgeon about any new lump. Our BBL recovery guide describes normal healing week by week.

How Is Fat Necrosis Diagnosed?

Your surgeon will ask when the lump appeared, whether it has changed and whether you have pain, fever or discharge, and will then examine the area. Fat necrosis can often be recognised by feel, but an ultrasound scan is the usual way to confirm it and rule out a seroma, haematoma or abscess.

At Centre for Surgery, an ultrasound scan is arranged off site when your surgeon needs one. It shows whether a lump is solid or fluid-filled, how large and deep it is and whether it is a simple oil cyst. In an imaging study of fat grafting, ultrasound was the best test for the oil cysts that commonly form after fat transfer, while MRI was better for more complex lumps^[7]. MRI is occasionally used for large or deep collections^[2], and drawing fluid from a cyst with a needle both confirms that it contains oil and treats it. A biopsy is rarely needed.

Does Fat Necrosis Go Away on Its Own?

Often, yes. Small areas of fat necrosis and small oil cysts commonly soften and shrink over 3 to 12 months as the body breaks down the dead fat, and some become small and unnoticeable without disappearing completely. Larger oil cysts and calcified lumps are less likely to resolve and may stay the same size for years unless they are treated.

As the dead fat is absorbed, the area can lose some volume and leave a slight dip or asymmetry, so a final judgement on shape is usually made at 6 months.

How to Get Rid of Fat Necrosis After a BBL

Treatment for fat necrosis after a BBL depends on the size of the lump, whether it is solid or fluid-filled, whether it hurts and how much it affects the shape of your buttocks. A review of fat necrosis after fat grafting describes the same stepped approach: whether to intervene depends on the nature of the nodule, and options range from simple aspiration to ultrasound-assisted liposuction or direct excision^[9].

Observation

Small, painless lumps are usually best watched at your follow-up reviews, with a repeat scan if the lump changes. Surgery on an area that is still settling can damage more of the surviving fat, so waiting is often right in the first few months.

Aspiration

Oil cysts and liquefied areas can be drained with a needle under local anaesthetic, often with ultrasound guidance. Some cysts refill and need more than one aspiration.

Liposuction

Firm areas of fat necrosis can be broken up and removed through small incisions. VASER liposuction suits dense, fibrous tissue and lets the surgeon smooth the contour around the lump.

Excision

Large, hard or calcified lumps can be cut out through a small incision. Excision leaves a scar and can leave a dent, so it is kept for lumps that are painful, visible or growing.

Refilling the area

Once the tissue has settled, any dent left behind can be corrected with further fat grafting as part of a revision BBL. At Centre for Surgery, patients with a concern are seen sooner for assessment, and revision is usually discussed at the 6-month review.

What about massage and home remedies?

There is no good evidence that creams, heat or supplements get rid of fat necrosis, and firm massage of the grafted buttocks in the first weeks can harm fat that is still establishing a blood supply. Centre for Surgery does not provide lymphatic drainage massage in-house; if your surgeon recommends it for swelling in the liposuction areas, you are referred to a qualified therapist and pay the therapist directly.

Will Fat Necrosis Ruin My BBL Result?

Usually not. Most fat necrosis is small, and where a lump or dent does affect the shape, the treatments above and a revision can usually restore a smooth contour.

Real Centre for Surgery patient, photographed at least six months after BBL surgery.

A smooth result like this depends on fat being placed in fine layers rather than large pools. See more results in our BBL before and after photos.

If you had your BBL elsewhere, including abroad, Centre for Surgery can assess lumps and contour problems and offer revision where appropriate; a different consultation fee applies and it is not redeemable. Our guide to BBL abroad explains why complications after surgery overseas can be harder to manage.

How to Prevent Fat Necrosis After a BBL

You cannot remove the risk completely, but most of the causes can be controlled. Some steps are down to your surgeon and some are down to you.

What your surgeon does: injects fat only into the subcutaneous layer above the gluteal muscle under real-time ultrasound, spreads it in thin threads with a blunt cannula and EVL, plans a volume your tissue can support rather than overfilling, and handles the fat gently during harvesting by power-assisted liposuction (PAL) or VASER.

What you can do:

• Stop nicotine: no smoking, vaping or nicotine replacement for 4 weeks before and 4 weeks after surgery.
• Keep pressure off the buttocks: no sitting directly on them for 2 weeks, with a BBL cushion if sitting is unavoidable. Keep toilet visits brief and lean forward.
• Sleep on your front or side: not on your back, for 2 weeks.
• Wear your compression garment: for 6 weeks day and night over the liposuction areas, with the buttocks left free.
• Build up activity gradually: walking from day 1 and light cardio from week 3, but nothing strenuous until 6 weeks.
• Attend your reviews: and report any new lump, redness or fever early.

When Should You Seek Help for a Lump After a BBL?

Contact your surgeon about any new or changing lump after a BBL. Most are harmless, but an early check means infection or a seroma can be treated before it affects your result.

Call 999 if you have sudden breathlessness, chest pain or are coughing up blood. These can be signs of a blood clot or fat embolism.

Call Centre for Surgery, or NHS 111 out of hours, if you have:

• a lump that is red, hot, swollen or increasingly painful;
• a fever, chills or feeling generally unwell;
• pus, a bad smell or oily fluid draining from a wound or the skin;
• darkening or breakdown of the skin over the buttocks;
• calf pain or swelling in one leg;
• a lump that is growing quickly.

For the first 24 hours you have your surgeon’s direct number, then the aftercare line is 020 7993 4849 (9am to 6pm, Monday to Saturday). Your wound check at 7 to 14 days, surgeon review at 6 weeks and reviews at 3 and 6 months are all chances to have a lump examined.

Frequently Asked Questions

Brazilian Butt Lift in London

BBL surgery at Centre for Surgery is performed by GMC-registered surgeons at our CQC-regulated Baker Street hospital, rated Good overall by the CQC. Every BBL uses real-time ultrasound to keep fat in the subcutaneous layer, and the operation is a day case under TIVA (total intravenous anaesthesia), with follow-up appointments included. The consultant who assesses you is the consultant who performs your surgery, and further consultations before surgery are free. We recommend a two-week cooling-off period before you go ahead. Finance isn’t available for BBL at Centre for Surgery, so the procedure is self-funded, and our BBL cost guide explains what is included. Your initial consultation is £100, redeemable against the cost of surgery if you go ahead.

Phone: 020 7993 4849 | Address: 95–97 Baker Street, Marylebone, London W1U 6RN
Contact us to schedule a consultation

References

1. Eto H, Kato H, Suga H, et al. The fate of adipocytes after nonvascularized fat grafting: evidence of early death and replacement of adipocytes. Plastic and Reconstructive Surgery 2012;129(5):1081–1092. doi:10.1097/PRS.0b013e31824a2b19 ↗
2. Masarapu V, Wang PS, Gorbachova T. Slow-growing buttock mass after failure of incorporation of autologous fat transfer for gluteal augmentation: ultrasound and MRI features. Skeletal Radiology 2020;49(10):1669–1675. doi:10.1007/s00256-020-03487-9 ↗
3. Milani Reis A, Roca Mora MM, Bicudo Bregion P, et al. Ultrasound-guided gluteal fat grafting: what is the evidence? A systematic review and meta-analysis. Aesthetic Surgery Journal 2025;46(1):57–62. doi:10.1093/asj/sjaf059 ↗
4. Domínguez-Millán R, Hoyos A, Cárdenas-Camarena L, et al. Non-embolic complications of gluteal fat transfer: a systematic review of the literature. Plastic and Reconstructive Surgery 2026. doi:10.1097/PRS.0000000000013408 ↗
5. Güzey S, Ergan Şahin A. Brazilian butt lift: what we learned over 7000 patients? Aesthetic Plastic Surgery 2026;50(14):5864–5872. doi:10.1007/s00266-026-05899-9 ↗
6. Elsaftawy A, Bonczar M, Jagosz M, et al. Gluteal augmentation with fat grafting: a systematic review and meta-analysis of complications and procedural factors. Plastic and Reconstructive Surgery 2025;157(3):381e–393e. doi:10.1097/PRS.0000000000012437 ↗
7. Costantini M, Cipriani A, Belli P, et al. Radiological findings in mammary autologous fat injections: a multi-technique evaluation. Clinical Radiology 2012;68(1):27–33. doi:10.1016/j.crad.2012.05.009 ↗
8. Sørensen LT. Wound healing and infection in surgery. The clinical impact of smoking and smoking cessation: a systematic review and meta-analysis. Archives of Surgery 2012;147(4):373–383. doi:10.1001/archsurg.2012.5 ↗
9. Dong M, Li F. Diagnosis and management of fat necrosis after autologous fat transplantation of breast [article in Chinese]. Chinese Journal of Reparative and Reconstructive Surgery 2021;35(7):918–922. doi:10.7507/1002-1892.202102052 ↗

Related Articles

• How To Prevent Dents After A BBL
• BBL Risks: Is a Brazilian Butt Lift Safe?
• Revision BBL
• BBL Recovery and Aftercare: A Week-by-Week Guide