Most bumps under the skin are harmless. The most common causes are cysts, lipomas (fatty lumps), swollen lymph nodes, and dermatofibromas, all of which are benign. At least 20% of adults will develop a cyst at some point in their lives, and lipomas are similarly widespread. That said, a few characteristics can help you tell a routine lump from one worth getting checked.
Cysts: The Most Common Culprit
A cyst is a small, round capsule filled with a mix of keratin (the protein that makes up your outer skin layer), oil, fluid, or pus-like material. They feel firm or slightly squishy and sit just beneath the surface. Cysts sometimes form after a skin injury, when a pocket of skin cells gets tucked inward and dead cells accumulate inside.
Cysts are completely benign. They commonly show up on the face, neck, chest, stomach, and back. They can stay the same size for years or slowly grow. The important thing: don’t try to pop or squeeze a cyst at home. Attempting to drain it yourself increases the risk of infection, and the cyst will almost always grow back because the capsule wall is still inside.
Lipomas: Soft, Rubbery Fat Lumps
If the bump feels soft and rubbery, moves easily when you press on it, and sits deeper than a typical pimple, it’s likely a lipoma. Lipomas are slow-growing collections of fat cells surrounded by a thin fibrous capsule. They don’t actually grow in the skin itself but in the fatty layer underneath it. Common locations include the shoulders, neck, stomach, chest, and back.
Lipomas are not cancerous. Most don’t need treatment unless they’re painful or bothersome. They can range from pea-sized to several centimeters across and tend to grow very slowly over months or years.
Swollen Lymph Nodes
If the bump is in your neck, under your chin, in your armpit, or in your groin, it may be a swollen lymph node. Lymph nodes swell when your immune system is fighting off an infection, and they often feel tender or painful to the touch. A cold, sore throat, or ear infection can trigger noticeable swelling that lasts a week or two and then resolves on its own.
Lymph nodes that deserve closer attention are those that feel hard or rubbery, don’t move when you push on them, keep growing over two to four weeks, or appear with no obvious infection. Unexplained weight loss, night sweats, or a persistent cough alongside swollen nodes also warrants a visit to your doctor.
Ganglion Cysts Near Joints
A firm, round bump on your wrist, hand, ankle, or foot is often a ganglion cyst. These grow out of a joint or the lining of a tendon and are filled with a thick, jellylike fluid similar to the lubricating fluid inside your joints. They look and feel like a small, firm water balloon. Ganglion cysts can fluctuate in size, sometimes shrinking and then swelling again with activity. They’re benign but can be uncomfortable if they press on a nearby nerve.
Dermatofibromas
Dermatofibromas are small, firm bumps that commonly appear on the legs. They’re tethered to the skin surface, so if you pinch the skin over one, it dimples inward rather than popping outward. This “dimple sign” is a classic way to identify them. They’re harmless, though they can be annoying. If one becomes ulcerated, changes color, or suddenly gets bigger, a doctor may remove it to rule out something more serious.
Abscesses and Infected Lumps
Not every under-skin bump is a quiet, slow-growing mass. An abscess is a pocket of pus caused by infection, and it behaves very differently from a cyst or lipoma. An abscess appears red and raised, feels warm and tender to the touch, and often hurts. The skin over the center may look thin, yellow, or white where pus is collecting just below the surface. Fever and chills can accompany a skin abscess, especially if the infection is spreading. Abscesses generally need to be drained by a healthcare provider rather than left to resolve on their own.
Vascular Bumps
Some under-skin bumps are made of blood vessels rather than fat or keratin. Hemangiomas, sometimes called strawberry marks because of their red color, feel firm and rubbery. Deeper ones that extend into the fatty layer can have a blue or purple tint and cause the skin to bulge outward. On darker skin tones, they may appear more brown or bruise-colored. Most vascular bumps are benign and present from birth or early childhood, though small cherry-red spots can develop in adults as well.
When a Bump Needs Medical Attention
The vast majority of subcutaneous lumps are harmless, but a few features should prompt you to get it looked at. Any new or changing spot that persists for more than two weeks is worth mentioning to a doctor. Lumps that grow rapidly, feel hard and fixed in place (they don’t slide around when you push), or measure 5 centimeters or larger (roughly the size of a golf ball) are flagged for further evaluation because the risk of malignancy increases with size and depth.
For spots on the skin’s surface, the ABCDE rule helps identify warning signs of melanoma: asymmetry, irregular borders, uneven color, diameter larger than about 6 millimeters (the size of a pencil eraser), and any evolution in size, shape, color, or behavior like itching or bleeding. A sore that won’t heal within two weeks or a mole that looks dramatically different from others on your body also deserves evaluation.
How Doctors Evaluate a Lump
For most small, soft, movable bumps, a physical exam is all that’s needed. Your doctor can often distinguish a lipoma from a cyst just by feeling it. When there’s uncertainty, an ultrasound is typically the first imaging step because it can show whether a mass is solid or fluid-filled and how deep it goes.
Lumps that sit deep beneath the muscle layer, measure 5 centimeters or larger, grow quickly, or appear without explanation are evaluated with advanced imaging, usually an MRI with contrast. If there’s concern about cancer, the biopsy is ideally performed by the specialist who would manage treatment, because where and how the biopsy is done matters for potential surgical planning down the line. Imaging is generally recommended before any biopsy so doctors have the full picture first.
Most people searching for “bump under my skin” are feeling something small, soft, and painless that appeared gradually. In the majority of cases, that description points to a cyst or lipoma, both entirely benign. Keeping an eye on its size and noting any changes over a few weeks gives you the clearest picture of whether it needs professional attention.