A lipoma is not actually a cyst, though the two are often confused. A lipoma is a slow-growing, benign tumor made of fat cells, enclosed in a thin fibrous capsule just beneath the skin. A cyst, by contrast, is a sac filled with fluid or dead skin cells. They feel different, form differently, and are treated differently. Because both show up as mysterious lumps under the skin, many people use the terms interchangeably, but understanding which one you have matters for knowing what to do next.
How Lipomas and Cysts Differ
Lipomas are solid masses of mature fat tissue. They feel soft, rubbery, and doughy when you press on them. They sit just under the skin and slide around easily when you push them with your finger. Most are smaller than two inches across, round or oval-shaped, and symmetrical. They don’t have an opening or visible pore on the skin’s surface.
Cysts form when dead skin cells accumulate under the skin, creating a small enclosed pocket surrounded by a lining. They can start out soft and painless but often become firmer over time. Many cysts have a tiny central opening (called a punctum) visible on the surface, which lipomas never have. Cysts can also become inflamed, red, or tender if they rupture internally or get infected, something lipomas rarely do.
A dermatologist can usually tell the difference during a physical exam. Lipomas, however, sometimes require removal and lab analysis to confirm the diagnosis under a microscope.
What Causes Lipomas
The exact cause isn’t fully understood, but genetics play a clear role. A condition called familial multiple lipomatosis runs in families through an autosomal dominant pattern, meaning a parent with the condition has a 50% chance of passing it to each child. Only one copy of the mutated gene is needed for the condition to appear.
Lipomas affect roughly 1 in 1,000 people and usually show up in early adulthood. They rarely appear in childhood. Some people develop just one; others develop several over time. Having one lipoma doesn’t necessarily mean you’ll get more, but some people are simply prone to them.
How Lipomas Are Identified
Most lipomas are diagnosed through a simple physical exam. The classic signs are a soft, movable lump that doesn’t cause pain. When the lump has typical features and is small, no imaging is usually needed.
Imaging becomes important when a lump is large, deep, firm, or growing. MRI is particularly useful here because it can reliably distinguish a simple lipoma from a liposarcoma, which is a rare cancerous tumor that also develops from fat tissue. On MRI, a simple lipoma appears as a uniform fatty mass with few or no internal dividers and no areas that light up with contrast dye. When those features are present, the scan is essentially diagnostic. Thickened internal dividers, irregular masses within the fat, or areas that enhance on imaging raise concern for something more serious.
When a Lump Needs Attention
The vast majority of lipomas are completely harmless. But certain characteristics warrant a closer look because liposarcomas can mimic lipomas early on. The key differences: liposarcomas tend to feel firm rather than soft, and they’re often fixed to deeper tissue rather than sliding freely under the skin. A lipoma that has stayed the same size for years is almost certainly benign. One that starts growing noticeably over weeks or months deserves evaluation.
Other reasons to have a lump checked include pain, swelling in the surrounding area, or limited range of motion in a nearby joint. These symptoms are uncommon with simple lipomas and can signal a different process.
Treatment and Removal
Most lipomas don’t require treatment. They’re benign, and if they’re not bothering you, leaving them alone is perfectly reasonable.
Removal becomes worth considering when a lipoma is painful, located in an area that causes discomfort (like under a waistband or bra strap), cosmetically bothersome, or large enough that it interferes with movement. Two main approaches are used:
- Surgical excision: The lipoma is cut out through an incision. This is the most common method and has a very low recurrence rate for simple lipomas. A technique called minimal excision extraction uses a smaller incision and results in less scarring.
- Liposuction: A needle and large syringe suction out the fatty tissue. This can be useful for larger lipomas or areas where a minimal scar is preferred, though it may not remove the capsule completely.
Simple lipomas rarely come back after complete surgical removal. Recovery from excision is generally straightforward, with bruising and some soreness at the site being the main side effects. Small lipomas removed in an office setting typically heal within one to two weeks. Larger or deeper lipomas removed in a surgical center may involve a slightly longer recovery, with possible fluid collection at the site that occasionally needs to be drained.
Multiple Lipomas
Some people develop dozens of lipomas over their lifetime. When this runs in families, it’s typically familial multiple lipomatosis. The lipomas in this condition behave the same as isolated ones: they’re benign, slow-growing, and soft. The main concern is cosmetic or physical discomfort from having many lumps. Each one can be removed individually if it causes problems, but new ones may continue to appear over time since the underlying genetic tendency remains.