Most lumps under the skin are harmless. Lipomas, cysts, swollen lymph nodes, and inflamed hair follicles account for the vast majority of bumps people notice, and many never need treatment. Still, understanding what different lumps feel like and when they deserve medical attention can save you a lot of worry.
Lipomas: The Most Common Cause
A lipoma is a slow-growing ball of fat that sits between your skin and the underlying muscle. It feels soft and rubbery, is usually round or oval, and slides easily under your fingers when you press on it. Most are smaller than two inches across, painless, and completely benign. They’re enclosed in a thin capsule, so they don’t spread into surrounding tissue.
Lipomas tend to run in families. If a parent or sibling has them, your odds go up. They can appear almost anywhere on the body but show up most often on the neck, shoulders, back, abdomen, arms, and thighs. Some people develop just one; others develop several over time. Certain inherited conditions cause lipomas to form in clusters across the body, but that’s uncommon. In most cases a single lipoma is nothing more than a cosmetic nuisance, and removal is optional.
Cysts: Firm and Sometimes Tender
Epidermal cysts (sometimes called sebaceous cysts) are another extremely common explanation for a lump you can feel under the skin. Unlike a lipoma, a cyst is a small sac filled with a thick, cheese-like material made of dead skin cells and oils. It forms when skin cells that normally shed outward instead migrate deeper and create a pocket beneath the surface.
The key differences from a lipoma are texture and mobility. A cyst tends to feel firmer and may not slide as freely because it’s often anchored to the skin above it. Many cysts have a tiny dark dot at the center, called a punctum, which is essentially a blocked pore opening. Cysts can stay the same size for years, but if they rupture internally or get infected, they become red, swollen, and painful quickly.
Never try to squeeze or pop a cyst at home. Doing so pushes material deeper into surrounding tissue, which can trigger infection or leave permanent scarring. If a cyst bothers you, a doctor can remove it with a small in-office procedure that takes out the entire sac, reducing the chance it comes back.
Swollen Lymph Nodes
If the lump you’re feeling is in your neck, under your chin, in your armpit, or in your groin, it may be a swollen lymph node rather than a growth. Lymph nodes are small, bean-shaped glands that filter fluid and trap bacteria and viruses. When your immune system is fighting something off, nearby nodes swell and can become tender to the touch.
The most common trigger is a garden-variety infection: a cold, strep throat, an ear infection, even an infected tooth. These nodes typically feel pea-sized to marble-sized, slightly tender, and they shrink back to normal within a couple of weeks once the infection clears. Widespread swelling of lymph nodes in multiple areas at once can signal a more systemic infection like mononucleosis or, less commonly, an autoimmune condition like lupus or rheumatoid arthritis.
Boils and Infected Hair Follicles
Some under-the-skin lumps are infections that start in or around a hair follicle. Folliculitis is a shallow infection that causes small, red, irritated bumps. When the infection goes deeper, it becomes a boil: a warm, painful lump that gradually fills with pus and may develop a white or yellowish center. A cluster of connected boils is called a carbuncle, which can leak fluid and cause more intense pain.
These lumps are hard to confuse with lipomas or cysts because they hurt, feel warm, look red, and develop over days rather than weeks or months. Most small boils drain on their own with warm compresses. Larger or persistent ones sometimes need to be drained by a healthcare provider, especially if surrounded by spreading redness, which can indicate a deeper skin infection.
Ganglion Cysts Near Joints
If you’ve noticed a firm, round bump on your wrist, hand, ankle, or foot, it could be a ganglion cyst. These are filled with a thick, jelly-like fluid and develop along tendons or joint capsules. A telltale feature is that they change size: they often get larger with repetitive joint movement and may temporarily shrink with rest. Some cause no symptoms at all, while others press on nearby nerves and create aching or tingling.
Ganglion cysts are benign. Many disappear on their own over time. If one is painful or interferes with movement, a doctor can drain the fluid with a needle or remove the cyst surgically, though they sometimes recur.
Less Common Causes
A handful of systemic conditions can produce lumps under the skin, though these are far less frequent than the causes above. Rheumatoid arthritis can cause firm, painless nodules on the extensor surfaces of joints, particularly the elbows and fingers. Gout deposits called tophi form hard lumps near joints after years of elevated uric acid. Autoimmune conditions like lupus, scleroderma, and dermatomyositis occasionally produce subcutaneous nodules as well. In each of these cases, the lumps rarely appear in isolation. They’re almost always accompanied by other symptoms like joint pain, skin changes, or fatigue that point toward the underlying disease.
Signs a Lump Needs Evaluation
The vast majority of lumps under the skin turn out to be benign, but a few characteristics should prompt you to get one checked. Pay attention if a lump is:
- Growing steadily over weeks, especially if it reaches two inches or more
- Hard and immobile, feeling fixed to deeper tissue rather than sliding freely
- Painless but persistent, particularly in the neck or near lymph node areas, without an obvious infection to explain it
- Changing in appearance, with overlying skin discoloration, ulceration, or irregular borders
Soft tissue cancers like sarcomas are rare, but they can initially look or feel like a harmless lump. Current referral guidelines recommend being seen within two weeks when a lump raises suspicion for malignancy, so don’t wait months hoping it resolves on its own if it matches the features above.
What Happens at the Doctor’s Office
For a new lump, the first step is usually a physical exam. A doctor can often distinguish a lipoma from a cyst or swollen lymph node just by feeling it and noting its location, texture, and mobility. When the diagnosis isn’t clear from touch alone, ultrasound is the most common next step for lumps close to the surface. It’s quick, painless, and effective at revealing whether a mass is solid or fluid-filled and how deep it extends.
If imaging raises any concern, or if the lump is large (generally five centimeters or more), an MRI may follow to better characterize the tissue. Biopsy is reserved for cases where imaging can’t rule out something more serious, and guidelines recommend completing imaging before any needle sampling so the results can guide where and how the biopsy is done. For the many lumps that turn out to be simple lipomas or cysts, the visit often ends with reassurance and a plan to monitor or remove the lump based on your preference.