Most cysts look like a small, round bump just under the skin, typically skin-colored or slightly yellow, and they feel smooth and firm when you press on them. They grow slowly, usually don’t hurt, and can range from pea-sized to several centimeters across. But “cyst” is a broad term, and the specific appearance depends on what type you’re dealing with and where it shows up on your body.
Epidermoid Cysts: The Most Common Type
The cyst most people picture when they search this question is an epidermoid cyst, sometimes incorrectly called a sebaceous cyst. These appear as well-defined, dome-shaped bumps in the skin, typically skin-colored to yellowish. Their signature feature is a central punctum: a tiny dark dot or pore on the surface, almost like a blocked pore. That punctum is the opening of the sac underneath.
These cysts are mobile, meaning you can push them around slightly under the skin with your finger. They feel firm but not rock-hard. You’ll most commonly find them on the face, neck, chest, stomach, or back. Inside, they’re packed with a protein called keratin (the same stuff your hair and nails are made of) mixed with dead skin cells. If one gets drained or ruptures, the material that comes out is thick, yellowish, and has a distinctly unpleasant smell. Despite the old name “sebaceous cyst,” they’re not actually filled with oil.
Pilar Cysts on the Scalp
Pilar cysts are close cousins of epidermoid cysts, but they grow from hair follicles and show up almost exclusively on the scalp. They feel like smooth, flesh-colored lumps under the skin. Unlike epidermoid cysts, pilar cysts lack that central punctum, so they look like a clean, round bump without any visible pore or opening.
These cysts can grow surprisingly large over time, occasionally reaching the size of a baseball, though most stay much smaller. They’re also filled with keratin, and it’s common to have more than one. Because they sit under the hair, many people discover them by feel rather than sight, noticing a firm, round lump while washing their hair.
Ganglion Cysts Near Joints
Ganglion cysts look and feel different from skin cysts. They appear as round or oval lumps near joints or tendons, most often on the top or underside of the wrist. You can also get them on hands, knees, or feet. They’re firm when you press on them, and the Mayo Clinic describes them as looking “like a tiny water balloon on a stalk” growing out of a joint lining.
Small ganglion cysts can be pea-sized, and some are so small you can’t even feel them. Their size often changes: they tend to get larger with repetitive joint movement and may shrink during periods of rest. Inside, they’re filled with a thick, jellylike fluid rather than the solid keratin found in skin cysts. The skin over a ganglion cyst usually looks completely normal, just raised.
How a Cyst Feels to the Touch
Touch is often more useful than sight for identifying a cyst. Epidermoid and pilar cysts are mobile under the skin. If you place your finger on one and push gently, you can slide it around a bit. This mobility is a key feature. Ganglion cysts, by contrast, are anchored to the joint or tendon they grew from, so they stay put when pressed, and they feel noticeably firm.
For comparison, a lipoma (a benign fatty lump) feels soft and doughy, almost like pressing into bread dough, and it also moves freely under the skin. The doughy quality is the main difference: cysts feel firmer and more defined, like a marble or small rubber ball beneath the surface. Both are typically painless unless they grow large enough to press on nearby nerves or other structures.
Cyst vs. Abscess
A cyst and an abscess can look similar at first glance since both create a visible lump, but they behave very differently. A cyst grows slowly over weeks or months, stays relatively the same color as surrounding skin, and generally doesn’t hurt. An abscess develops quickly, turns red, feels warm and tender to the touch, and is filled with pus from an active infection. An abscess often causes symptoms beyond the lump itself, like fever or general achiness.
If a bump appeared suddenly, is painful, and the skin around it looks red and swollen, that pattern points more toward an abscess or an infected cyst than a simple cyst on its own.
Signs a Cyst May Be Infected or Inflamed
A typical cyst sits quietly under the skin for months or years without causing problems. When one becomes inflamed or infected, the changes are hard to miss. The skin over and around the cyst turns red and feels warm. The lump becomes tender or painful, sometimes seemingly overnight. It may swell to several times its original size as fluid and pressure build inside.
An infected cyst can also start to drain on its own. The discharge is usually thick, off-white or yellowish, and carries a strong odor from the decomposing keratin and cellular debris inside. If the redness starts spreading outward from the cyst in streaks, or you develop a fever, that suggests the infection is moving beyond the cyst itself.
When a Lump Doesn’t Look Like a Typical Cyst
Certain features make a lump less likely to be a simple cyst. Lumps that feel deep, don’t move when pressed, and seem stuck to the tissue underneath are more concerning. A bump that’s hard as a rock, has an irregular shape rather than a smooth round contour, or grows rapidly over just a few weeks doesn’t fit the typical cyst profile. Skin changes over the lump, like dimpling, ulceration, or color changes beyond mild redness, also warrant a closer look.
Most lumps under the skin turn out to be benign, but a healthcare provider can usually distinguish a cyst from something else with a physical exam alone, and occasionally with an ultrasound if the diagnosis isn’t clear from touch and appearance.