A sebaceous cyst looks like a round, dome-shaped bump just beneath the skin’s surface. Most are small, typically under two inches in diameter, and they often match your skin tone or appear slightly yellowish. The bump feels firm to the touch and can usually be moved around slightly with your fingers, which is one of its most recognizable traits.
Shape, Color, and Surface Features
The classic sebaceous cyst is a smooth, round lump that raises the skin into a small dome. The overlying skin usually looks normal, though it can take on a slightly yellowish or whitish tint if the cyst sits close to the surface. One of the most distinctive features is a tiny dark dot near the center of the bump. This is called a punctum, and it marks the plugged opening of the hair follicle where the cyst formed. Not every cyst has a visible punctum, but when it’s there, it’s a strong clue you’re looking at a cyst rather than something else.
Most cysts start small, around the size of a pea, and grow very slowly over weeks to months. Some stay that size indefinitely. Others gradually enlarge to the size of a marble or golf ball, though reaching several inches across is uncommon.
How It Feels to the Touch
Pressing on a sebaceous cyst, you’ll notice it feels firm but not rock-hard. There’s a slight give to it, like pressing on a rubber ball. The cyst sits in the layer just below the skin, so it moves when you push on it. This mobility is a key characteristic. The bump isn’t anchored to the muscle or bone underneath.
When a cyst is not inflamed, it’s usually painless. You might not even notice it until you run your fingers over the area and feel the lump.
Where They Typically Appear
These cysts show up most often on the scalp, face, ears, neck, back, trunk, and groin area. They develop in places with hair follicles and oil glands, so they won’t appear on your palms or the soles of your feet. Finding a firm, movable bump in any of these common spots is a typical presentation.
What’s Inside
Despite the name, most “sebaceous cysts” are technically epidermoid cysts. The term sebaceous cyst has largely fallen out of clinical use. The difference matters because what’s inside isn’t actually sebum (skin oil) in most cases. Instead, the sac fills with keratin, the same protein that makes up your outer skin and nails. This material is thick, paste-like, and whitish-yellow. If a cyst ruptures or is squeezed, the discharge often has a notably unpleasant, cheese-like smell. That distinctive odor is another hallmark that separates these cysts from other lumps.
What an Inflamed or Infected Cyst Looks Like
A calm, stable cyst blends in fairly well. An inflamed one does not. When a cyst becomes irritated or infected, the skin over it turns red or pink, and the area swells noticeably, sometimes to double the original size within a day or two. The bump becomes warm and tender, and pressing on it causes real pain. You may notice a thick, yellowish or greenish discharge if the cyst starts to drain, along with that strong odor from the keratin contents mixing with pus.
Inflammation can happen when the cyst wall ruptures under the skin, even without any obvious injury. The keratin material leaks into surrounding tissue and triggers a strong immune response. This is why a cyst that sat quietly for months can suddenly become angry and swollen seemingly overnight.
How to Tell It Apart From Similar Lumps
A few other skin lumps can look similar at first glance, but each has distinguishing features.
- Lipoma: A lipoma is a fatty lump that also sits under the skin and moves when pressed. The key difference is texture. Lipomas feel soft and doughy, almost squishy, while cysts feel firmer. Lipomas also lack the central punctum and are almost always painless, even when pressed.
- Abscess (boil): An abscess is a pocket of pus caused by infection. It appears pink or red from the start, feels swollen and painful, and develops quickly over days rather than weeks or months. A cyst, by contrast, typically grows slowly and only becomes red and painful if it gets inflamed. Abscesses also tend to feel warmer and more tender than an uninfected cyst.
- Enlarged lymph node: Swollen lymph nodes can feel like firm lumps, but they appear in specific locations (neck, armpit, groin) and are usually associated with illness or infection elsewhere in the body. They don’t have a punctum and aren’t as mobile as a cyst.
In most cases, a healthcare provider can distinguish between these possibilities just by examining the lump’s shape, firmness, and mobility. Imaging is rarely needed unless the lump is unusually large or in an atypical location.
Changes Worth Paying Attention To
A stable, painless cyst that hasn’t changed in months is generally not a concern. The signs that warrant a closer look include rapid growth over a short period, increasing redness and pain, recurrent drainage, or a lump that feels fixed in place rather than movable. A cyst that keeps coming back after draining on its own may need complete surgical removal of the sac wall to prevent recurrence, since the cyst will refill as long as the lining remains intact.