A cyst is a closed sac of tissue that can form nearly anywhere in your body, filled with fluid, pus, air, or semi-solid material. Most cysts are benign, slow-growing, and painless. They range from tiny pockets you’d never notice to large lumps you can feel under your skin or masses that show up on an imaging scan during a routine checkup.
What a Cyst Looks and Feels Like
A cyst near the surface of your skin typically feels like a firm, round lump that moves slightly when you press on it. Small cysts are often painless. You may not notice one until it grows large enough to press on surrounding tissue, at which point it can become tender or uncomfortable. Some cysts stay the size of a pea for years; others slowly expand over months.
Cysts are distinct from solid tumors because they contain an enclosed sac with liquid or semi-solid contents rather than a dense mass of cells. They also differ from abscesses, which are acute infections filled with pus that cause redness, swelling, and significant pain. A cyst can become infected and turn into an abscess, but on its own it’s typically not red or warm to the touch.
Common Types and Where They Form
Epidermoid cysts are by far the most common type, accounting for roughly 80 to 90 percent of all skin cysts. They develop when skin cells that normally shed get trapped beneath the surface and accumulate inside a sac. You’ll find them most often on the face, neck, and trunk.
Ganglion cysts form along tendons or joints, especially in the wrist and hand. They’re filled with a thick, jelly-like fluid and can fluctuate in size depending on your activity level. Baker’s cysts develop behind the knee, usually as a result of cartilage damage or arthritis pushing fluid into a pocket at the back of the joint. Ovarian cysts are extremely common in people who menstruate, often forming during the normal ovulation cycle and resolving on their own within a few weeks. Kidney cysts, particularly simple ones, become more frequent with age and rarely cause symptoms.
Why Cysts Form
Cysts develop through several different mechanisms depending on where they are. Skin cysts usually result from a blocked duct or hair follicle. When oil or dead skin cells can’t drain normally, they build up inside a pocket that gradually expands. Chronic inflammation, injury to the skin, or a history of acne can all increase the likelihood of this happening.
Internal cysts often have different origins. Ovarian cysts form as part of the menstrual cycle when a follicle doesn’t release an egg or doesn’t dissolve afterward. Kidney cysts can develop when small segments of the kidney’s filtration tubes grow abnormally and fill with fluid, eventually detaching from the surrounding tissue. In some cases, obstruction of a duct or tube creates a backup of fluid that balloons into a cyst over time.
Genetics play a role in certain cyst-related conditions. Polycystic kidney disease, for example, is caused by inherited gene mutations that affect proteins responsible for normal cell growth in the kidneys. People with these mutations typically develop multiple kidney cysts between the ages of 30 and 50.
How Cysts Are Diagnosed
Your doctor can often identify a skin cyst through a physical exam alone. The location, texture, and mobility of the lump provide strong clues. When a cyst is deeper inside the body, or when your doctor needs to confirm that a mass is fluid-filled rather than solid, imaging is the standard next step. Ultrasound, CT scans, and MRI can all distinguish a simple cyst from a tumor by showing its internal structure, including whether it contains liquid, solid material, or a mix of both.
If imaging reveals a straightforward, fluid-filled sac with smooth walls, it’s almost certainly benign. No further testing is needed in most cases, though your doctor may recommend periodic imaging to track any changes. Blood tests can also be useful. With kidney cysts, for instance, a blood sample can reveal whether the cyst is large enough to affect how well the kidney filters waste.
Treatment: When and How Cysts Are Removed
Many cysts need no treatment at all. If the cyst is small, painless, and not growing, your doctor will likely suggest monitoring it over time. This “watchful waiting” approach is especially common for simple kidney cysts and small ovarian cysts that are expected to resolve on their own.
When a cyst becomes bothersome, two main options exist: drainage and surgical removal. During drainage, a doctor numbs the area with a local anesthetic, makes a small incision, and lets the fluid out. The procedure is quick, but the cyst often returns because the sac lining is still in place. Surgical removal is more definitive. The surgeon takes out the entire cyst, including the surrounding sac, and closes the skin with stitches. Removing the sac significantly reduces the chance of recurrence.
For internal cysts, the approach depends on the organ involved. A kidney cyst causing pain can occasionally be drained with a needle inserted through the skin, after which the empty space is filled with a solution to prevent the cyst from refilling. Ovarian cysts that persist, grow large, or cause significant symptoms may require a minimally invasive surgical procedure.
Why You Should Never Pop a Cyst at Home
Squeezing or puncturing a cyst yourself introduces bacteria directly into the tissue beneath your skin. With ganglion cysts, the risk is even more serious. Because a ganglion cyst connects directly to a joint, popping it at home can push bacteria into the joint space, potentially causing a severe joint infection that’s far more dangerous than the cyst itself. Even with skin cysts, home drainage almost always leads to incomplete removal, infection, scarring, or the cyst growing back larger than before.
What Happens If a Cyst Ruptures
A ruptured skin cyst is usually just messy and mildly painful. Internal cysts are a different story. A ruptured ovarian cyst can cause sudden, sharp pain in the lower abdomen or back, vaginal spotting, and bloating. Most ruptured ovarian cysts heal without intervention, but complications can be serious. If the cyst was infected, rupture can trigger sepsis, a life-threatening immune response. A large or heavy cyst can also cause the ovary to twist on itself, cutting off its blood supply, which requires emergency surgery.
Seek immediate medical attention for a ruptured cyst if you experience severe nausea and vomiting, fever, heavy vaginal bleeding, or dizziness and faintness. These symptoms suggest a complication that won’t resolve on its own.
Signs a Cyst May Need Urgent Attention
The vast majority of cysts are harmless, but certain changes warrant a prompt visit to your doctor. Rapid growth or a sudden change in size is the most important signal. Pain or tenderness that develops in a previously painless cyst, redness or warmth over the area, and any unusual discharge are also red flags.
On imaging, features that raise concern for malignancy include irregular walls, internal dividers (called septations), and solid components mixed in with the fluid. The fluid itself can be telling: benign cysts typically contain clear or straw-colored liquid, while suspicious cysts may contain bloody, dark brown, or cloudy fluid caused by dead cells or disrupted blood vessels. Your doctor may recommend additional imaging or a biopsy if any of these features appear.