What Is a Lipoma? A Plain-English Guide to Soft, Fatty Lumps Under the Skin

You felt a soft lump under your skin, and now your mind is racing through worst-case scenarios. Before you panic, take a breath: that squishy, movable bump is very often a lipoma, one of the most common and harmless lumps people develop.

A lipoma is a benign (noncancerous) growth made of fat cells. Most never cause problems and never need treatment. Still, it's worth knowing what they are, how to recognize one, and the few situations where a lump is worth showing to a clinician.

What is a lipoma, exactly?

A lipoma is a benign, slow-growing tumor made of mature fat cells (adipocytes). It usually sits in the subcutaneous tissue, the layer between your skin and the muscle underneath. "Tumor" sounds alarming, but here it simply means a growth of cells, not cancer.

You can often recognize a lipoma by how it feels. It's typically soft, doughy, and rubbery, and it moves easily when you press it with a fingertip. The skin over it looks normal, and most lipomas are painless. They are the most common benign soft tissue tumor in adults. They're common enough that roughly 1 in every 1,000 people develops one at some point, though precise incidence figures haven't actually been established in the medical literature.

• Soft, doughy, or rubbery to the touch
• Moves easily under the skin with light pressure
• Usually painless
• Normal-looking skin on top, not tethered or discolored
• Grows slowly over months to years

What causes lipomas, and who gets them?

The exact cause of lipomas isn't fully understood. They tend to run in families, which points to genetic factors. They most commonly appear between the ages of 40 and 60 and can affect both sexes.

Most people with a lipoma have just one. But about 5 to 10% of patients develop multiple lipomas, which can sometimes be linked to genetic syndromes such as familial multiple lipomatosis, Gardner syndrome, PTEN hamartoma syndrome, Proteus syndrome, or MEN type 2B. Lipomas are most often found on the trunk and upper arms, and they're somewhat more common in people with high blood lipids (hyperlipidemia), type 2 diabetes, or obesity.

How big do lipomas get, and how fast?

Lipomas grow slowly, often so gradually that you may not notice a change from month to month. Most stay smaller than about 1 to 2 inches (3 to 5 cm) across. That said, they can range from roughly the size of a pea to more than 10 cm, and they can keep slowly enlarging over time.

Size alone doesn't make a lipoma dangerous. A bigger lump is still usually benign. But a lipoma that grows quickly, becomes firm or fixed in place, or starts to hurt is worth having checked, because those features are less typical of a simple lipoma.

Lipoma vs. cyst vs. something more serious

Lots of lumps live under the skin, and they can be hard to tell apart on your own. A lipoma is fatty, soft, and movable. A sebaceous or epidermoid cyst, by contrast, often sits closer to the skin's surface, may have a central pore, and can become red or tender if it gets inflamed.

The growth most people quietly worry about is cancer. A lipoma is not cancer and is typically harmless. Rarely, a malignant fatty tumor called a liposarcoma can mimic a lipoma, which is one reason a lump that is painful, rapidly growing, hard, or fixed to deeper tissue deserves a professional evaluation. A clinician can examine it and, if needed, order imaging or a biopsy to be sure.

How are lipomas treated?

For most lipomas, the best treatment is none at all. Since they are harmless and usually painless, doctors generally leave them alone and simply keep an eye on them.

Removal is an option when a lipoma is painful, growing, pressing on nearby nerves, or simply bothersome (including for cosmetic reasons). The two main approaches are surgical excision and liposuction.

• Surgical excision: removes the entire lipoma, including its capsule. Completely excised subcutaneous lipomas have a low recurrence rate of about 1 to 2%.
• Liposuction: less invasive and may leave a smaller scar, but it can fragment the lipoma and leave fat behind, raising the chance it comes back.
• Deep lipomas (for example, those that sit within muscle) are generally harder to remove completely and tend to recur more often than simple subcutaneous ones.

When should you see a doctor?

Most lipomas never need a visit beyond peace of mind. But it's worth getting any new or changing lump evaluated, especially the first time you notice one, so you can confirm what it is.

See a clinician promptly if a lump becomes painful, grows quickly, feels hard or fixed in place, changes the look of the overlying skin, or comes back after removal. These features don't mean something is definitely wrong, but they're the signs worth checking rather than guessing about at home. If a lump grows rapidly over days, becomes severely painful, or appears alongside warmth, spreading redness, and fever, seek urgent medical care.