A cyst under the skin typically looks like a small, round bump that rises slightly from the surface. Most are skin-colored or have a faint yellowish or whitish tint, feel soft to the touch, and range from a few millimeters to several centimeters across. The key visual clue is a tiny dark dot at the center of the bump, which is the opening where the cyst connects to the skin’s surface.
What You’ll See on the Surface
Most skin cysts sit just beneath the outer layer of skin, creating a dome-shaped lump that’s smooth and well-defined. The skin over a healthy, non-inflamed cyst usually looks completely normal in color. Because the cyst is filled with a soft material (primarily a protein called keratin, not oil or fluid), the bump tends to look rounded rather than irregular. Small cysts can be as tiny as a pea. Larger ones may stretch the skin enough to give the area a slightly shiny or taut appearance.
The most distinctive visual feature is a small central pore, sometimes called a punctum. This looks like a tiny blackhead or dark pinpoint right at the center of the lump. Not every cyst has a visible one, but when it’s there, it’s a strong sign you’re looking at an epidermoid cyst rather than another type of lump.
How a Cyst Feels When You Touch It
Press gently on a cyst and it will feel soft, smooth, and slightly squishy. Unlike a swollen lymph node or a hard tumor, a cyst gives a little under your finger. One helpful test: try to move it. A typical epidermoid cyst stays fixed in its position in the skin but slides freely over the deeper tissue underneath. It feels like a marble that’s attached to the skin layer but not anchored to muscle or bone.
Cysts are usually painless unless they become inflamed. You might not notice one for months or even years until it grows large enough to feel through your clothing or catch your eye in a mirror.
What’s Inside
Despite being commonly called “sebaceous cysts,” most skin cysts aren’t actually filled with oil. They’re filled with keratin, the same protein that makes up your hair and nails. This material accumulates inside a sac lined with skin cells, building up in layers over time. If a cyst ruptures or is drained, what comes out is thick, yellowish, and cheese-like in texture, often with a strong, unpleasant smell. That foul odor is one of the hallmarks of a ruptured cyst and is completely normal for this type of lump.
When a Cyst Becomes Inflamed
An inflamed or infected cyst looks dramatically different from a calm one. The skin over it turns red, feels warm, and the area swells noticeably. The lump becomes tender or outright painful to touch, and it may grow rapidly over a few days. Sometimes a yellowish or greenish discharge leaks from the central pore.
This inflammation often happens when the cyst wall ruptures beneath the skin, spilling its keratin contents into the surrounding tissue. Your body treats that material as a foreign invader and mounts an immune response, which produces the redness and swelling. This can look identical to a bacterial infection, and sometimes bacteria are involved too, making it difficult to tell the difference without a professional evaluation.
Types That Look Different
Not all cysts under the skin look the same. The type depends on where it forms and what it’s made of.
- Epidermoid cysts are the most common. They appear on the face, neck, chest, and back, and they’re the ones most likely to have that visible central pore. They grow slowly and can stick around for years.
- Pilar cysts form on the scalp. They look and feel similar to epidermoid cysts but typically lack the central punctum. They tend to be firmer and smoother, and they often run in families.
- Ganglion cysts develop near joints and tendons, most commonly on the wrist or hand, followed by the ankles and feet. They’re round or oval, can be as small as a pea, and their size often fluctuates, getting larger with repeated joint movement. Unlike epidermoid cysts, ganglion cysts are filled with a thick, jelly-like fluid and feel firm. They’re also fixed in place, anchored to the joint or tendon beneath them, so they don’t slide around when you press on them.
Cyst vs. Lipoma
The lump most commonly confused with a cyst is a lipoma, which is a benign collection of fat cells. Both feel soft and sit under the skin, but there are reliable differences. A lipoma tends to feel doughy or rubbery and spreads wider under the surface, while a cyst feels more like a defined ball. Lipomas usually sit deeper, between the skin and the muscle layer, while cysts live in the skin itself. Lipomas also lack that central punctum and won’t produce any discharge if squeezed. Both are overwhelmingly benign, but they’re treated differently, so distinguishing between them matters if you’re considering removal.
Signs That Need Attention
Most cysts are harmless and can sit under your skin indefinitely without causing problems. But certain changes warrant a closer look. Rapid growth over weeks rather than months, a hard or irregular texture, pain without obvious inflammation, or a lump that’s firmly fixed to the tissue beneath it (not just the skin above) are all reasons to get it checked. A cyst that keeps coming back after being drained may need complete surgical removal of the sac lining to prevent recurrence. And any lump that changes noticeably in size, shape, or color deserves professional evaluation to rule out something other than a simple cyst.