A benign cyst is a closed, sac-like pocket of tissue that can fill with fluid, semi-solid material, or air. It is not cancerous and does not spread to other parts of the body. Cysts are extremely common, can form nearly anywhere, and most are completely harmless. Many people have cysts without ever knowing it.
What a Cyst Looks Like and Feels Like
Most benign cysts feel like a smooth, round bump just under the skin. They can be as tiny as a pinhead or grow to several inches across. A sebaceous cyst (also called an epidermoid or pilar cyst), one of the most familiar types, typically appears on the face, neck, chest, stomach, or back and ranges from less than a sixteenth of an inch to about four inches in diameter. Ganglion cysts, which form on joints or tendons, tend to be smaller, usually a quarter inch to about an inch and a quarter, and show up most often on the hands, knees, or feet.
Some cysts are painless and only noticeable when you happen to feel them. Others cause discomfort if they press on a nerve, sit near a joint, or become infected. The texture varies by type: a ganglion cyst feels firm and rubbery, while a sebaceous cyst is usually softer and slightly movable under the skin.
Common Types and Where They Form
Cysts are named for where they develop or what they contain. Here are the types people encounter most often:
- Sebaceous (epidermoid) cysts: Round bumps filled with a thick, cheese-like material called keratin. Common on the face, neck, chest, and back.
- Ganglion cysts: Fluid-filled lumps that grow on top of joints or tendons, especially in the wrists and hands.
- Ovarian cysts: Fluid-filled sacs on or inside the ovaries. In a large screening study of women over 55, simple ovarian cysts appeared in 14% of women at their first ultrasound, and about 8% developed a new one each year. Many resolve on their own: among women who had a cyst at their first screen, 32% had no cyst a year later.
- Dermoid cysts: Painless lumps that often show up near the eyebrows, on the scalp, chest, or collarbone. They can contain unusual tissue like hair or skin cells because they form from cells present since embryonic development.
- Pilomatrixoma: A small, hard, calcified bump typically found on the head, neck, or arms, usually less than an inch and a quarter across.
Kidney cysts are also very common, particularly after age 50, and are usually discovered incidentally during imaging for something else. Internal cysts like these rarely cause symptoms unless they grow large enough to press on surrounding tissue.
Why Cysts Form
Cysts develop for several reasons, depending on the type. The most common cause is a blocked duct or gland. When a gland that normally releases oil or fluid gets clogged, the material backs up and forms a sac. This is how most sebaceous cysts begin.
Infections and chronic inflammation can also trigger cyst formation. When tissue is irritated or damaged repeatedly, the body sometimes walls off the affected area, creating a fluid-filled pocket. Injuries that damage small blood vessels or break hair follicles can seed a cyst the same way.
Some cysts have a genetic component. Polycystic kidney disease, for example, results from inherited gene mutations that cause the lining of the kidney’s tiny tubes to grow abnormally and secrete excess fluid, gradually forming clusters of cysts. These conditions typically become apparent between ages 30 and 50. Other developmental cysts, like dermoid cysts, trace back to cells that were displaced during fetal growth and only become noticeable later in life.
How Doctors Tell a Cyst Is Benign
When you find a lump, the first goal is to confirm it’s a simple cyst and not a solid tumor. Ultrasound is the most common tool for this. On an ultrasound image, a classic benign cyst has a few telltale features: it appears completely dark inside (no internal echoes, meaning it’s filled with clear fluid), it has a well-defined, smooth border with a sharp edge separating it from surrounding tissue, and it produces a bright column of sound behind it, called posterior enhancement.
Shape matters too. Benign masses tend to be wider than they are tall when viewed on ultrasound, sitting parallel to the skin surface. By contrast, features that raise concern include irregular, spiky margins radiating outward from the mass, internal debris or solid components, and a shape that grows taller than it is wide. If any of these suspicious features are present, your doctor may recommend further imaging or a biopsy to rule out something more serious.
For cysts you can see and feel, like a sebaceous or ganglion cyst, a physical exam is often enough for a diagnosis. A doctor can usually identify these by location, texture, and appearance alone.
Treatment and Removal
Many benign cysts need no treatment at all. If a cyst is small, painless, and not bothering you, the standard approach is simply to leave it alone and monitor it over time.
Treatment becomes an option when a cyst hurts, gets infected, limits your movement, or bothers you cosmetically. There are two main approaches:
Drainage is the simpler option. After numbing the area with a local anesthetic, a provider makes a small cut in the skin, drains the contents, then covers the site with gauze and a bandage. The procedure is quick and provides immediate relief, but because the cyst wall stays in place, the cyst can refill and come back later.
Surgical removal is more definitive. The provider numbs the area the same way, then makes a slightly larger incision and removes the entire cyst, including its lining. The opening is closed with stitches. Because the sac itself is gone, the chance of recurrence is much lower. Recovery is straightforward for most surface cysts. You’ll have a small wound that needs to be kept clean, and stitches typically come out within one to two weeks.
Internal cysts, like ovarian or kidney cysts, follow a different path. Small, simple ovarian cysts often resolve without intervention. Larger or persistent ones may be removed laparoscopically, a minimally invasive surgery using small incisions and a camera. Kidney cysts that cause symptoms can be drained with a needle guided by imaging or, less commonly, surgically removed.
Signs a Cyst Needs Attention
Most cysts sit quietly for months or years without changing. But certain changes warrant a closer look. Contact your doctor if you notice any new lump that doesn’t go away after several days or keeps growing, pain or tenderness at the site, swelling or redness around the cyst, warmth or skin discoloration that suggests infection, or changes in a cyst you’ve had for a while, such as a sudden increase in size or a shift in how it feels. Infected cysts can become abscesses if left untreated, so redness and pain together are worth addressing promptly.