Most lumps you can feel under your skin are benign. Lipomas, cysts, dermatofibromas, and swollen lymph nodes account for the vast majority of these bumps, and each one has a distinct feel that can help you figure out what you’re dealing with. Here’s what the most common types are, how to tell them apart, and which characteristics deserve a closer look.
Lipomas: The Most Common Culprit
Lipomas are the most common soft tissue tumors, occurring in roughly 1% of the general population. They’re made of mature fat cells sitting just beneath the skin, and they have a very recognizable feel: soft, doughy, and painless. If you press on one, it moves easily under your finger. Doctors sometimes call this the “slippage sign,” where the lump seems to glide away when you slide your fingers across it.
Most lipomas range from 1 to 10 centimeters, though they occasionally grow larger. They favor fatty areas of the body, particularly the trunk, neck, forearms, and upper arms and thighs. They’re rarely found on the hands or feet. Lipomas tend to grow slowly over months or years, and many people have them for a long time before noticing. They don’t change the skin above them, so the surface looks completely normal.
A related type called an angiolipoma contains small blood vessels in addition to fat. Unlike regular lipomas, angiolipomas can be painful because tiny blood clots form in those vessels near the outer wall of the lump.
Cysts: Firm With a Central Pore
Epidermoid cysts (often called “sebaceous cysts,” though that’s technically a misnomer) are another extremely common type of under-skin lump. They feel different from lipomas. Rather than soft and squishy, a cyst is firm and compressible, like pressing on a small rubber ball. They typically range from half a centimeter to several centimeters across.
The giveaway feature is a tiny dark dot at the center, called a punctum. This is a small pore opening in the skin directly over the lump. If a cyst ruptures or gets squeezed, it can release a yellowish, cheese-like material with a strong, unpleasant smell. That material is keratin, the same protein that makes up your hair and nails. When a cyst ruptures beneath the skin surface, the surrounding tissue becomes inflamed, red, and tender, which is often when people first notice one.
Cysts vs. Abscesses
A cyst that suddenly becomes hot, red, swollen, and painful may have become infected, turning into something closer to an abscess. The distinction matters. A cyst is a closed sac that’s usually harmless and not contagious. An abscess is a pocket of pus caused by bacterial infection. It appears pink or red, feels swollen and painful, and the pus it contains is highly contagious. If a lump you’ve had for a while rapidly becomes warm and tender over a day or two, infection is the likely reason.
Dermatofibromas: Small, Firm, and Pigmented
Dermatofibromas are the most common painful tumor of the skin, though “painful” here is relative. Most are mildly tender rather than truly painful. They present as small, firm nodules, usually on the arms or legs, measuring 5 to 15 millimeters across. In lighter skin, they appear pink to light brown. In darker skin, they can look dark brown to black, sometimes with a paler center.
The hallmark test is the “dimple sign.” If you pinch the skin on either side of the lump, the surface dimples inward rather than popping outward. This happens because the nodule is tethered to the skin surface but moves freely over the deeper tissue beneath it. Dermatofibromas are completely benign and often develop after a minor injury like an insect bite, though many appear without any obvious trigger.
Swollen Lymph Nodes
Lymph nodes are small, bean-shaped glands that filter fluid and trap infections throughout your body. You normally can’t feel them. When they swell, they become palpable lumps, most commonly in the neck, under the chin, in the armpits, and in the groin. Many lymph nodes are concentrated in the head and neck, which is why a sore throat or ear infection often produces noticeable lumps along the jawline or behind the ears.
The most common cause is a viral infection like the common cold. Ear infections, infected teeth, skin infections like cellulitis, and mononucleosis all trigger lymph node swelling in nearby areas. Swollen nodes from infection are typically tender, slightly movable, and shrink back to normal once the infection clears. If lymph nodes swell throughout your body at once (neck, armpits, and groin simultaneously), systemic infections like mononucleosis or HIV are possible causes.
How to Tell These Apart by Feel
- Soft, doughy, painless, slides under your finger: likely a lipoma
- Firm, round, has a tiny dark dot on the surface: likely an epidermoid cyst
- Small, firm, on a limb, dimples when you pinch it: likely a dermatofibroma
- Tender, appeared during an illness, in the neck/armpit/groin: likely a swollen lymph node
- Hot, red, rapidly painful, appeared over days: possibly an abscess or infected cyst
Features That Warrant a Closer Look
Size is one of the most important factors. Soft tissue lumps larger than 5 centimeters receive more scrutiny because larger growths have a higher statistical association with concerning diagnoses. A lump that grows noticeably over weeks, rather than staying stable for months or years, also raises the threshold for further evaluation. Imaging guidelines generally recommend investigation when a mass increases by more than 20% in volume or diameter over six months.
Mobility matters too. Benign lumps like lipomas and cysts move freely when you push on them. A lump that feels fixed in place, as though it’s attached to the muscle or bone beneath it, is less typical of common benign growths. Similarly, lumps that are rock-hard rather than firm or doughy, lumps with irregular edges rather than smooth borders, and lumps that cause pain without signs of infection all deserve professional assessment.
For swollen lymph nodes specifically, the key timeline is persistence. Nodes that swell during a cold and shrink within a week or two are behaving normally. Nodes that don’t go away, continue growing over time, or cause severe pain should be evaluated. The same applies to any lump: stable and unchanged for years is reassuring, while rapid growth or new symptoms is not.
What Evaluation Looks Like
For most lumps, a physical exam is the starting point. Many lipomas and cysts can be identified by feel alone. When there’s uncertainty, ultrasound is typically the first imaging step. It can distinguish between solid masses and fluid-filled cysts, measure precise dimensions, and help guide the next decision.
If imaging raises questions, a core needle biopsy (where a small sample of tissue is extracted through a needle) provides a definitive answer. This is generally preferred over fine needle aspiration because it gives more tissue to analyze. A biopsy is recommended when a mass is new on imaging, growing beyond expected parameters, or when the physical exam is suspicious regardless of what imaging shows.