A sebaceous cyst is a slow-growing, round lump beneath the skin that’s filled with a buildup of protein and dead skin cells. Despite the name, most of these cysts have nothing to do with your sebaceous (oil) glands. The medical term doctors actually use is “epidermal inclusion cyst” or “epidermoid cyst,” because the contents are keratin and cell debris, not the oily sebum your skin produces for moisture. The name “sebaceous cyst” stuck in everyday language, but understanding what’s really going on inside helps explain how these lumps behave, why they come back, and when they need attention.
Why the Name Is Misleading
Your skin constantly sheds old cells as new ones push up from below. Normally those dead cells flake away on their own. A cyst forms when something disrupts that process: a scratch, a surgical wound, acne, or chronic sun damage can trap skin cells beneath the surface instead of letting them exit. Those cells and the protein keratin accumulate inside a sac, creating a firm, slow-growing lump.
Because the cyst is packed with keratin rather than oil, calling it “sebaceous” is technically wrong. Most healthcare providers reserve the term “sebaceous cyst” for a specific condition called steatocystoma multiplex, where the cysts genuinely fill with sebum. But since nearly everyone searches for “sebaceous cyst,” that’s the term you’ll see on patient education sites and even in some doctor’s offices.
How These Cysts Form
The most common trigger is a blocked hair follicle. At the top of each follicle is a small funnel-shaped opening. When that opening gets plugged, dead skin cells that would normally travel up and out get rerouted underneath the skin’s surface. Your body walls them off inside a thin sac, and the lump slowly grows as more cells accumulate inside.
Cysts can also appear in areas without many hair follicles. Any injury or trauma that pushes surface skin cells down into the deeper layer of skin (the dermis) can seed a cyst. This is why you might notice one forming near an old scar, a piercing site, or a spot where you had surgery years ago.
The face, neck, upper back, and chest are the most common locations, but they can show up essentially anywhere on the body. They tend to be more common in adults than children, and people with a history of acne or frequent skin injuries are somewhat more prone to developing them.
What They Look and Feel Like
A typical cyst is a dome-shaped bump ranging from pea-sized to several centimeters across. The skin over it usually looks normal, though you may notice a tiny dark dot at the center, sometimes called a punctum, which marks the blocked follicle opening. The lump feels firm but slightly movable when you press on it. It rolls under your fingertip rather than feeling anchored to the tissue below.
If the cyst ruptures or gets squeezed, it can release a thick, whitish or yellowish material that often has a strong, unpleasant smell. That’s the keratin and dead cell buildup, not pus (unless infection is involved). Most cysts are completely painless unless they become inflamed or infected.
Cysts vs. Lipomas
People often confuse cysts with lipomas, and it’s easy to see why. Both are common lumps under the skin. The key differences come down to texture and depth. A cyst feels firm and is anchored closer to the skin surface, often with that visible punctum. A lipoma is a collection of fat cells that sits deeper, between the skin and muscle. Lipomas feel soft and doughy, almost rubbery, and they tend to be wider and flatter. Lipomas almost never become painful or infected, while cysts occasionally do. If you’re unsure which you’re dealing with, a doctor can usually tell the difference with a simple physical exam.
When a Cyst Gets Inflamed or Infected
A cyst that’s been stable for months or years can suddenly become red, swollen, warm, and tender. This happens in two ways. Sometimes the cyst wall ruptures internally, spilling keratin into the surrounding tissue. Your immune system reacts to that material as if it were a foreign invader, triggering inflammation even though no bacteria are involved. Other times, bacteria do get in, usually through the punctum or after someone tries to squeeze the cyst at home, and a true infection develops.
The distinction matters because inflammation without infection often responds to a steroid injection that calms the immune reaction, while a genuine bacterial infection may need antibiotics or drainage. Signs that point toward infection include increasing pain, spreading redness, warmth radiating outward from the lump, and sometimes fever. An inflamed cyst that’s simply irritated tends to stay more localized.
Treatment Options
If a cyst isn’t bothering you, no treatment is necessary. Many people live with small cysts for years without any problems. The main reasons to have one removed are cosmetic concerns, discomfort from its location (a cyst under a bra strap or waistband, for example), or repeated episodes of inflammation.
The standard treatment is surgical excision, a minor in-office procedure done under local anesthesia. The surgeon makes a small incision, removes the entire cyst including its sac wall, and closes the site with a few stitches. Complete removal of that sac is the critical step. If any part of the wall is left behind, the cyst can refill and come back. A large study of over 2,100 surgically removed cysts found a complication rate of only about 2.2%, with the most common issues being minor wound problems or scarring.
A quicker alternative is incision and drainage, where the doctor makes a small cut, squeezes out the contents, and lets the site heal. This provides fast relief, especially for an inflamed cyst, but it carries a higher chance of recurrence because the sac wall is still in place. Think of it as emptying a balloon without popping it: the balloon can fill up again.
Home Care
Applying a warm, damp cloth to the area for 15 to 20 minutes a few times a day may help a mildly inflamed cyst feel more comfortable and could encourage fluid to drain into the surrounding tissue. There’s no strong clinical evidence that warm compresses resolve cysts on their own, but they can reduce discomfort while you wait for a medical appointment. The one thing you should avoid is squeezing or popping a cyst yourself. This can push material deeper into the skin, introduce bacteria, and turn a painless lump into a painful, infected one.
Multiple Cysts and Genetic Links
Most people who get a cyst develop one or two over a lifetime. Developing many cysts, especially at a young age, can occasionally signal a genetic condition. Steatocystoma multiplex is an inherited disorder caused by a mutation in a gene involved in skin cell structure. People with this condition develop dozens of small, true sebaceous cysts (filled with actual oil) across the chest, arms, and other areas. It’s closely related to another inherited skin condition called pachyonychia congenita, which also involves abnormal cyst growth along with thickened nails. These conditions are uncommon but worth knowing about if multiple cysts seem to run in your family.
What to Expect Long Term
Cysts that are completely excised, sac and all, rarely come back. Cysts that are only drained or partially removed have a meaningful chance of recurring in the same spot, sometimes months or even years later. A cyst that has been inflamed or infected multiple times often develops more scar tissue around it, which can make future removal slightly more involved.
These lumps are almost always benign. Malignant transformation is extremely rare, to the point that routine biopsy of a typical, uncomplicated cyst isn’t considered necessary. That said, any lump that grows rapidly, feels fixed to deeper tissue, or looks very different from the firm, movable bump described here is worth having evaluated to rule out other possibilities.