A cyst under the skin typically looks like a small, round, flesh-colored or yellowish bump, usually between 1 and 3 centimeters across. Most feel firm but slightly compressible, move freely when you push on them, and grow slowly enough that you might not notice one for weeks or months. What a cyst looks like in detail depends on the type, where it is on your body, and whether it has become inflamed.
The Classic Appearance of a Skin Cyst
The most common type, an epidermoid cyst, shows up as a dome-shaped nodule that sits just beneath the skin’s surface. The skin over it usually looks normal or has a slight yellowish tint. One hallmark feature is a tiny dark dot at the center called a punctum, essentially a blocked pore. Not every cyst has one, but when it’s there, it’s a reliable clue that you’re looking at a cyst rather than something else. If you squeeze the area (which isn’t recommended), a thick, white or yellowish, cheese-like substance with a strong odor can come out of that central opening.
These cysts show up most often on the face, neck, upper back, and shoulders. They’re fixed to the skin itself, meaning the skin moves with them, but they slide freely over the muscle and tissue underneath. That mobility is one of the easiest ways to identify a cyst at home.
How Different Cyst Types Compare
Pilar Cysts
Pilar cysts grow almost exclusively on the scalp, developing from hair follicles. You’ll usually discover one while washing or combing your hair. They feel smooth and round under your fingers and are flesh-colored, blending in with the surrounding skin. Unlike epidermoid cysts, they lack a visible punctum. Pilar cysts grow slowly but can eventually reach surprising sizes, sometimes as large as a baseball if left alone for years. If you have one, there’s a good chance others will develop over time.
Ganglion Cysts
These appear near joints and tendons, most commonly on the wrist or hand, and less often on the ankles and feet. A ganglion cyst looks like a round or oval lump filled with a jelly-like fluid. Small ones can be pea-sized, while larger ones are clearly visible under the skin. Their size often fluctuates, growing larger with repeated joint movement and sometimes shrinking on their own. They have a distinctive appearance, almost like a tiny water balloon sitting on top of a joint.
Cyst vs. Lipoma
The lump most commonly confused with a cyst is a lipoma, a soft, fatty growth between the skin and muscle. Both are usually painless and harmless, but they feel noticeably different. A cyst is firm and somewhat compressible, anchored to the skin above it. A lipoma is softer and more rubbery, sits deeper, and slides around easily under your fingernail with gentle pressure. Lipomas also lack the central punctum that many cysts have, and they never produce discharge.
If a deeper lump feels hard or fixed in place rather than mobile, that’s a different situation worth getting checked. With lipomas specifically, rapid growth, a size over 10 centimeters, or a location deep in the thigh are features that prompt imaging to rule out something more serious.
What an Infected or Inflamed Cyst Looks Like
A cyst can become inflamed even without an infection. When that happens, the area around it turns red or, on darker skin tones, noticeably darker. The bump swells, feels warm, and becomes tender or outright painful to the touch. You might notice it doubles in apparent size over just a day or two.
An infected cyst takes this further. The redness spreads, the pain intensifies, and you may see yellowish or greenish fluid draining from the surface. The discharge often has a strong, unpleasant smell. A ruptured cyst, one that breaks open beneath the skin, can trigger a boil-like reaction with significant swelling and pain that needs prompt attention. Any cyst that was previously painless and suddenly becomes hot, swollen, or starts draining has likely become inflamed or infected.
When a Lump May Not Be a Cyst
Most lumps under the skin turn out to be benign, but certain features suggest something other than a simple cyst. Pay attention if a lump grows rapidly over weeks rather than months, feels hard and fixed to deeper tissue rather than mobile, or changes in color or texture. A bump that bleeds without being injured or keeps coming back after being removed also warrants evaluation.
Multiple cysts appearing in unusual locations like the fingers or toes can be associated with Gardner syndrome, a genetic condition linked to colon cancer. This is uncommon, but if you’re developing cysts in places where they don’t typically appear, it’s worth mentioning to a healthcare provider. A single, slow-growing, mobile lump with a central punctum on your back or neck is, in the vast majority of cases, exactly what it looks like: a harmless cyst.