Lipomas form when fat cells overgrow into a soft, rubbery lump beneath the skin, and in most cases, there’s no single clear cause. They affect roughly 1 in 1,000 people and usually appear in early adulthood, though they can develop at any age. The growth is almost always benign, enclosed in a thin fibrous capsule, and completely separate from the normal fat tissue around it.
While researchers haven’t identified one definitive trigger, several factors make lipomas more likely to develop. Understanding those factors can help you make sense of why a lump appeared and whether it’s something to keep an eye on.
What Happens Inside a Lipoma
A lipoma starts when the stem cells responsible for producing fat cells begin behaving abnormally. Research from Karger Publishers found that the stem cell pool inside lipomas shows altered patterns of cell growth, cell death, and the ability to generate new cells. In practical terms, this means a small cluster of fat cells starts multiplying faster than it should while also resisting the normal signals that would tell those cells to stop growing or die off.
The result is a slow-growing mass of mature fat cells wrapped in a thin capsule of connective tissue. That capsule is what gives lipomas their characteristic feel: soft, movable, and clearly separated from the tissue around them. Most lipomas stay under 5 centimeters (about 2 inches) and grow so slowly that people often can’t pinpoint when they first appeared.
Genetics and Family History
If your parent or sibling has lipomas, your chances of developing them go up. A condition called familial multiple lipomatosis causes people to grow numerous lipomas, sometimes dozens, across the torso, arms, and legs. It follows an autosomal dominant inheritance pattern, meaning you only need to inherit the altered gene from one parent to be affected. A parent with the condition has a 50% chance of passing it to each child.
The specific gene responsible hasn’t been identified yet, according to the National Institutes of Health. Even outside of this inherited condition, lipomas clearly run in families. If you develop one lipoma, you have a higher-than-average chance of developing more over time, especially if relatives have had them too.
Risk Factors That Increase Your Chances
Beyond genetics, several factors are consistently linked to lipoma development:
- Age: Lipomas most commonly surface between ages 40 and 60, though they can form earlier.
- Obesity: Carrying excess body fat doesn’t directly cause lipomas, but it’s associated with a higher likelihood of developing them. Notably, losing weight doesn’t shrink existing lipomas because the encapsulated fat behaves independently from regular body fat.
- Physical trauma: Some lipomas appear at sites of previous injury. The connection isn’t fully understood, but localized tissue damage may trigger abnormal fat cell growth in certain people.
- Other medical conditions: Diabetes, high cholesterol, and liver disease have all been linked to higher rates of lipoma formation.
Conditions That Cause Multiple Lipomas
Most people with a single lipoma have nothing else going on medically. But multiple painful lipomas can signal a less common condition worth knowing about.
Dercum’s disease causes painful fatty growths, typically on the trunk, upper arms, and upper legs. The pain can be severe, sometimes from the lipomas pressing on nearby nerves or from inflammation in the surrounding connective tissue. People with Dercum’s disease often also experience fatigue, generalized weakness, easy bruising, memory and concentration problems, and depression. The condition has been linked to autoimmune dysfunction, hormonal disturbances, and problems with how the body processes fat, though its exact cause remains unknown. High-dose corticosteroid use and certain infections have been identified as potential triggers.
Madelung disease, another rare condition, causes large symmetrical fat deposits around the neck, shoulders, and upper arms. It’s strongly associated with heavy alcohol use and is far more common in men. Gardner syndrome, a genetic disorder, can cause lipomas alongside other growths throughout the body.
When a Lump Needs a Closer Look
The vast majority of lipomas are harmless and never become cancerous. However, liposarcoma, a rare cancer of fat tissue, can sometimes be mistaken for a lipoma in its early stages. MD Anderson Cancer Center offers a useful rule of thumb for telling them apart: lipomas are soft and squishy, and you can push them around with your fingers. Liposarcomas tend to feel firm and are fixed in place because they attach to deeper tissue.
Size and growth rate matter more than the lump’s mere existence. A lump that has sat unchanged on your arm for years is far less concerning than one that starts growing noticeably over weeks or months. If a lump that was one size at Thanksgiving is clearly bigger by New Year’s, that’s worth getting checked. The same goes for any lump that becomes painful, feels hard, or can’t be moved under the skin.
Doctors typically diagnose lipomas through a physical exam alone. If there’s any uncertainty, an ultrasound or MRI can confirm whether the mass is made of fat. A biopsy, where a small tissue sample is examined under a microscope, is reserved for lumps with unusual features.
Can You Prevent Lipomas?
There’s no proven way to prevent lipomas from forming. Because the root cause involves changes in how fat stem cells behave, and because genetics play such a strong role, lifestyle changes alone won’t reliably stop them. Maintaining a healthy weight and staying physically active support overall health, but they won’t eliminate your risk if you’re genetically predisposed.
If you already have lipomas and they aren’t bothering you, treatment is optional. Most people choose to leave them alone. Surgical removal is straightforward when a lipoma causes pain, grows large enough to be uncomfortable, or sits in a cosmetically bothersome spot. Recurrence after removal is uncommon but possible, particularly in people who are prone to developing multiple lipomas.