Most lumps under the skin are harmless. Lipomas, cysts, and swollen lymph nodes account for the vast majority of subcutaneous bumps people discover, and none of these require urgent treatment. Still, the type of lump matters, and a few characteristics can help you figure out what you’re dealing with and whether it needs attention.
Lipomas: The Most Common Culprit
Lipomas are round or oval lumps made of fatty deposits that sit between the skin and the deeper tissue beneath it. They’re soft, usually painless, and move easily when you press on them. Doctors sometimes check for what’s called a “slippage sign,” where the lump slides out from under your fingers when you push gently across its edge. That easy movement is a hallmark of lipomas and distinguishes them from lumps that are anchored to deeper tissue.
The skin over a lipoma looks completely normal. They tend to show up on the forearms, torso, and back of the neck, and they range from pea-sized to several centimeters across. Most lipomas don’t need treatment at all. If one becomes bothersome because of its size or location, surgical removal usually cures it permanently. Other options include steroid injections, which shrink the fatty tissue, and liposuction, though liposuction rarely eliminates a lipoma completely.
Cysts: Firm Bumps With a Visible Dot
Epidermal inclusion cysts (often called sebaceous cysts, though that name is technically inaccurate) are round, dome-shaped bumps filled with keratin, a protein your skin naturally produces. They’re not filled with oil, despite what many people assume. True sebaceous cysts filled with oily sebum are actually quite rare.
A telltale feature is a small dark dot, called a punctum, in the center of the cyst. They range from about a quarter-inch to over two inches across. Unlike lipomas, cysts feel firmer and don’t slide around as freely because they’re tethered to the surrounding skin. They’re generally painless unless they become infected or inflamed, at which point they can turn red, swell, and hurt.
Ganglion Cysts Near Joints
If the lump is near your wrist, hand, ankle, or foot, it may be a ganglion cyst. These grow out of a joint lining or tendon sheath and look like small, firm water balloons. No one knows exactly why they form. Their size can change over time, often growing larger with repeated joint movement. Ganglion cysts are benign and sometimes resolve on their own, though they can be drained or surgically removed if they cause discomfort or interfere with movement.
Swollen Lymph Nodes
Lymph nodes are small, bean-shaped glands that filter fluid and fight infection. When they’re doing their job, they swell, and you can suddenly feel them under your skin. The most common places to notice a swollen lymph node are the neck (along the front, sides, and back), under the jaw and chin, behind the ears, in the armpits, and in the groin.
Swollen lymph nodes usually signal that your body is fighting an infection, anything from a cold to a dental issue. They typically shrink back to normal within a couple of weeks once the infection clears. In children, a lymph node larger than 1 centimeter (about the width of a pencil eraser) is considered enlarged. A node that persists for weeks without an obvious cause, keeps growing, or feels hard and immovable warrants a closer look.
Dermatofibromas
These are small, firm, brownish to red-purple bumps that commonly appear on the legs. They’re made up of a buildup of soft tissue cells under the skin and sometimes itch. Dermatofibromas are usually only 0.5 to 1 centimeter across. A useful test: gently pinch the skin around the bump from both sides. A dermatofibroma will dimple inward rather than popping outward. This “dimple sign” is one of the most reliable ways to identify them without any tools. They’re harmless and don’t require treatment unless they bother you cosmetically.
Infected Lumps and Abscesses
An abscess is a pocket of pus caused by a bacterial infection. On the skin, it appears pink or red, feels warm to the touch, and is usually swollen and painful. Unlike a cyst, which develops slowly and sits quietly, an abscess comes on relatively quickly and gets worse. You may also experience fever, chills, fatigue, or loss of appetite if the infection is significant. An existing cyst can also become infected, turning what was once a painless bump into something red and tender. Abscesses generally need to be drained and may require antibiotics.
When a Lump Needs Urgent Evaluation
The vast majority of subcutaneous lumps are benign, but a small percentage are not. UK clinical guidelines recommend treating any lump as potentially serious if it meets several specific criteria: larger than 5 centimeters (about 2 inches), located deep in the body rather than just under the skin, increasing in size, and painful. Even with all four features present, the actual risk of malignancy is only about 3 to 4 percent, but that’s enough to justify prompt evaluation at a specialist center.
A few details are worth keeping in mind. Increasing size is the single best individual indicator of concern. A mass that grows slowly over weeks to months is more worrying than one that balloons overnight (rapid growth over days is more likely to be infectious or inflammatory). The common belief that only painful lumps are dangerous is wrong. Soft tissue cancers typically present as large, painless masses that have been quietly growing. Hard texture, irregular edges, and attachment to deeper structures are additional red flags that set concerning lumps apart from the soft, smooth, movable ones described above.