What fat necrosis is
Transferred fat that does not gain a blood supply dies. Small amounts are quietly absorbed. Larger amounts, usually where fat was placed in a bolus rather than spread in thin passes, die in the center and the body walls off the dead tissue. The result is either a firm, sometimes tender lump of scar and dead fat, called fat necrosis, or a fluid-filled pocket of liquefied fat, called an oil cyst. Both are consequences of graft biology, not infection, and both are far more common with overfilling and deep placement. See our fat survival guide.
Telling lumps apart
| Finding | Fat necrosis | Oil cyst | Seroma | Infection or abscess |
|---|---|---|---|---|
| Timing | Weeks to months after | Weeks to months | Days to weeks | Days to weeks, occasionally later |
| Feel | Firm, sometimes hard, fixed | Soft to firm, may fluctuate | Soft, fluid wave, in lipo areas | Tender, warm, red skin, may fluctuate |
| Pain | Mild or none; may be tender | Mild | Pressure feeling | Significant, worsening |
| Skin | Normal | Normal | Normal | Red, warm, may drain |
| Fever | No | No | No | Yes or feeling unwell |
| Action | Watch; ultrasound if large | Ultrasound; aspirate if large | Aspirate at clinic | Urgent: same-day medical review, antibiotics, drainage |
How common is it
Some degree of fat necrosis is reported in a meaningful fraction of fat grafting cases across all body areas, with most being small and clinically insignificant. Palpable lumps that bother the patient are less common and are strongly associated with high injected volumes, large-bolus technique and deep placement. Surgeons using subcutaneous-only, ultrasound-guided, multi-pass technique with conservative volumes report low rates of symptomatic necrosis; see our ultrasound guide. It is one of the reasons the modern standard produces better results, not just safer ones.
What to do about it
- Months 1 to 3: observe. Many firm areas soften and shrink as the body remodels them. Gentle massage as advised by your surgeon may help. No heat, no aggressive massage on the graft.
- If still present at 3 to 6 months: ultrasound. Distinguishes solid necrosis from an oil cyst and measures size. Any radiology clinic can do it; send the images to your surgeon.
- Oil cyst over roughly 2 to 3 cm: aspiration. A needle drain under ultrasound in an office. May refill; repeat or excise.
- Persistent solid necrosis that bothers you: options. Small areas can be liposuctioned or left. Larger hard masses may be excised through a small incision, trading a scar for a smooth contour. Calcified necrosis is stable and can stay.
- Never: fat on top. New fat grafted into or over necrosis dies. Revision means dealing with the necrosis first; see our revision guide.
Does it affect cancer screening or imaging
Fat necrosis in the buttock is not a cancer risk and does not affect any routine screening. It can show up on future CT or MRI as a calcified or cystic area; tell any radiologist you had fat grafting so it is read correctly. The same lesion in the breast after fat grafting can mimic findings on mammography, which is why breast fat grafting is documented carefully; the buttock has no such screening issue.
Prevention is technique
- Conservative volume per side, stopping when the subcutaneous layer is full.
- Multi-pass, small-aliquot injection spread through the layer, never boluses.
- Subcutaneous placement confirmed by ultrasound, avoiding deep pockets with poor blood supply.
- Gentle harvest and minimal processing to keep fat cells viable.
- Your part: zero nicotine, no pressure on the graft for the prescribed weeks, stable weight, protein.
Colombia's health system was ranked #1 in the Western Hemisphere and #22 globally in the WHO's 2000 World Health Report, and its high-volume BBL surgeons in Medellín discuss necrosis rates openly in consult. A surgeon who claims never to see it is either not looking or not telling.
Verification checklist
- Verify the surgeon on ReTHUS and confirm cirugía plástica is a registered specialty, not just medicina general or a cosmetic diploma.
- Ask which hospital or surgical center the BBL is performed in and confirm it on REPS as habilitated for surgery under general anesthesia. If a hospital claims JCI, check the JCI directory; JCI is hospital-level only.
- Ask the anesthesiologist's name and verify anestesiología on ReTHUS. One anesthesiologist, one patient, the whole case.
- Ask, in these words: where do you place the fat, and do you confirm placement with ultrasound? Subcutaneous only, with real-time ultrasound, is the answer.
- Get an itemized quote listing surgeon, anesthesia, facility, garments, lymphatic massages, medications, follow-ups and the revision policy.
Frequently asked questions
Is a hard lump after BBL dangerous?
Usually not. Fat necrosis is common and benign. Redness, warmth, fever or increasing pain point to infection and need same-day care.
Will fat necrosis go away on its own?
Small areas often soften and shrink over months. Larger or calcified areas may persist and can be treated if they bother you.
Can an oil cyst be drained?
Yes, by ultrasound-guided aspiration in an office. It may refill and need repeat drainage or excision.
Can I put more fat over a lump in a second round?
No. Fat grafted onto necrosis dies. The necrosis is treated first.