A skin cyst is a small, closed sac that forms just beneath the surface of your skin, filled with a protein called keratin and dead cell debris. Most skin cysts are completely benign, grow slowly, and never become dangerous. They feel like a firm, round marble under the skin and range from pea-sized to several centimeters across. While they’re sometimes called “sebaceous cysts,” that name is actually misleading, since the vast majority aren’t filled with oil at all.
How a Skin Cyst Forms
Your skin is constantly shedding old cells as part of its normal life cycle. These cells travel outward through hair follicles and fall away. A cyst forms when something disrupts that process, trapping cells beneath the surface instead of letting them shed normally.
The most common trigger is damage to a hair follicle. A scratch, surgical wound, acne, or even chronic sun damage can block the top portion of a follicle, creating a pocket where dead skin cells and keratin start to collect. Over weeks or months, a thin wall of skin tissue grows around this material, forming a self-contained sac. The cyst keeps growing because the lining continues producing keratin with nowhere for it to go.
The Three Main Types
Not all skin cysts are identical. The type depends on where in the skin the sac originates.
- Epidermoid cysts are by far the most common. They develop from the upper portion of a hair follicle or from the outer layer of skin itself. You’ll find them most often on the face, neck, chest, and back. They’re encapsulated in a thin layer of tissue that resembles normal skin and are filled with keratin and fatty debris.
- Pilar cysts develop deeper, from the root of the hair follicle. About 90% of pilar cysts show up on the scalp. They tend to run in families and feel slightly firmer than epidermoid cysts.
- True sebaceous cysts are actually rare. They arise from the oil-producing glands attached to hair follicles. Despite the name being used loosely for almost any skin cyst, genuine sebaceous cysts make up a small fraction of cases.
What a Cyst Looks and Feels Like
A typical skin cyst is a smooth, round bump you can move freely under the skin with your fingers. It’s usually skin-colored or slightly yellowish. Many have a tiny dark dot at the center called a punctum, which is the blocked opening of the hair follicle where the cyst originated. That punctum is one of the easiest ways to identify a cyst on your own.
Most cysts are painless. You might not even notice one until it grows large enough to feel through clothing or catch on a collar or waistband. The contents, if they ever drain on their own, tend to be a thick, yellowish, paste-like material with a noticeable smell. That’s the keratin and cell debris breaking down inside the sac.
Cyst vs. Lipoma vs. Abscess
Three types of lumps under the skin get confused with each other regularly, but they’re quite different.
A lipoma is a soft, doughy collection of fat cells. It moves easily under the skin, just like a cyst, but it lacks a punctum and feels softer. Lipomas almost never become painful or inflamed on their own.
An abscess is a pocket of pus caused by a bacterial infection. Unlike a cyst, an abscess develops quickly (often over days), and the surrounding skin is warm, red, swollen, and painful. If a lump appeared suddenly and hurts to touch, that pattern points toward an abscess rather than a cyst.
The punctum is the key detail. If you can spot a small central pore on the bump, it’s most likely a cyst. If the area is hot and angry, infection is involved, whether it started as a cyst or not.
When a Cyst Becomes Inflamed or Infected
A cyst can sit quietly under your skin for years without causing trouble. Problems start when the cyst wall ruptures internally. This doesn’t mean the cyst breaks through the skin surface. Instead, the thin sac tears inside, releasing keratin into the surrounding tissue. Your immune system treats that keratin like a foreign invader, triggering redness, swelling, tenderness, and sometimes significant pain. This is an inflammatory reaction, not necessarily an infection, though bacteria can take advantage of the situation and turn it into one.
An infected cyst looks similar to an abscess: the area becomes red, warm, and painful, and you may notice pus draining from the punctum. Squeezing or picking at a cyst is one of the most common ways to cause a rupture or introduce bacteria, which is why dermatologists strongly advise against it.
Treatment Options
Small, painless cysts that aren’t bothering you don’t require treatment. Many people live with them indefinitely without any issues. Treatment becomes relevant when a cyst is painful, inflamed, in a cosmetically sensitive area, or large enough to interfere with daily life.
Drainage
A doctor can make a small incision and squeeze out the contents, which provides quick relief if a cyst is swollen and uncomfortable. The downside is that drainage leaves the cyst wall intact beneath the skin. Because that lining keeps producing keratin, the cyst often refills over time. Drainage is best thought of as a temporary fix.
Surgical Excision
The only way to permanently remove a cyst is to take out the entire sac, lining and all. This is a minor outpatient procedure. After numbing the area with a local anesthetic, the doctor makes a small incision, removes the intact cyst in one piece, and closes the wound with stitches. The whole process typically takes 15 to 30 minutes. You’ll have a small scar, but the cyst is far less likely to return. When the sac is left behind, even partially, the cyst can fill right back up.
Timing Matters
If a cyst is actively inflamed or infected, most doctors prefer to treat the inflammation first, sometimes with antibiotics or drainage, and schedule excision for after things have calmed down. Removing an inflamed cyst is harder because the tissue is swollen and fragile, which increases the chance of leaving part of the wall behind.
What You Can Do at Home
If a cyst becomes tender or mildly inflamed, warm compresses are the standard home approach. Apply a warm, wet washcloth to the area for 20 to 30 minutes, three to four times a day. The warmth encourages circulation and can help the inflammation settle. Use water that’s comfortably warm, not hot enough to burn your skin.
Beyond that, the most important thing you can do is leave the cyst alone. Don’t squeeze it, scratch it, lance it, or try to drain it yourself. Puncturing a cyst at home can push existing infection deeper into the skin, trigger severe bleeding, or cause the internal wall to rupture, making the problem significantly worse. If a cyst is growing, painful, or showing signs of infection like redness and warmth, that’s the point where a doctor’s involvement makes the difference between a simple fix and a recurring problem.