A cyst is a closed sac of tissue that can form anywhere in your body. These sacs are usually filled with fluid, pus, air, or semi-solid material, and most are benign. They range from tiny pockets you’ll never notice to large growths that cause pain or interfere with organ function. The word is sometimes spelled “cist,” but the correct medical spelling is “cyst.”
How Cysts Form
Cysts develop when something disrupts the normal flow of fluid or cell growth in a tissue. The most straightforward cause is a blocked duct or gland. When oil, mucus, or other fluid can’t drain properly, it accumulates in a pocket that slowly expands. This is what happens with many skin cysts and some kidney cysts.
Chronic inflammation can also trigger cyst formation. Repeated irritation causes tissue to wall itself off, creating a self-contained sac. Infections sometimes produce cysts as the body tries to contain damaged tissue. Genetic factors play a role too, particularly in conditions like polycystic kidney disease, where inherited mutations cause cells lining the kidney’s tiny tubes to multiply abnormally and secrete excess fluid, forming clusters of cysts over time.
Common Types and Where They Appear
Cysts show up in predictable locations depending on their type:
- Epidermoid and sebaceous cysts form just beneath the skin, often on the face, neck, or trunk. They’re firm, round bumps filled with a thick, yellowish material made of skin cells and oils.
- Ovarian cysts develop on or inside the ovaries. Many are functional, meaning they form as part of the normal menstrual cycle and resolve on their own within a few weeks.
- Ganglion cysts appear as rubbery lumps near joints, most commonly on the wrist, fingers, or feet. They contain a thick, jelly-like fluid from the joint lining.
- Acne cysts form deep in the skin when pores become severely blocked and inflamed. These are among the most painful skin cysts.
Less common varieties include cysts in the kidneys, liver, breasts, and brain. Pancreatic cysts are often found incidentally during imaging for other conditions. Baker’s cysts form behind the knee, usually related to arthritis or cartilage damage.
Cyst vs. Tumor vs. Abscess
A lump under your skin or inside your body could be a cyst, a tumor, or an abscess, and they’re not the same thing. A cyst is a fluid-filled sac with a defined wall. A tumor is a solid mass of abnormal tissue, which can be benign or cancerous. An abscess is a pocket of pus caused by infection, typically warm, red, and painful.
On ultrasound or CT scan, a simple cyst appears as a uniform, fluid-filled circle with thin walls. This appearance is almost always benign. If a cyst contains solid components mixed with fluid, it needs closer evaluation because some complex cysts can be malignant. A biopsy, where a small tissue sample is removed and examined under a microscope, is the most reliable way to determine whether any growth is cancerous.
How Cysts Are Diagnosed
Many cysts near the surface are diagnosed with a simple physical exam. Your doctor can often tell a skin cyst from a tumor by feeling its texture and mobility. For internal cysts, imaging is essential. Ultrasound is typically the first step because it’s fast, widely available, and excellent at distinguishing fluid-filled structures from solid ones.
When ultrasound can’t fully characterize a cyst, MRI provides a more detailed picture. This is especially true for larger masses (10 cm or more in diameter) or cysts in complex locations. For ovarian cysts found incidentally on imaging, size and appearance determine whether follow-up is needed. Simple ovarian cysts under 5 cm in premenopausal women and under 3 cm in postmenopausal women generally don’t require monitoring at all. If a cyst looks the same on imaging over two or more years, the chance of malignancy is essentially ruled out by that stability alone.
Do Cysts Go Away on Their Own?
Many do. Functional ovarian cysts frequently resolve within one to three menstrual cycles without any treatment. Ganglion cysts have a well-documented tendency to disappear spontaneously. In adults, 40% to 58% of ganglion cysts resolve without intervention. In children, the rate is even higher, ranging from 48% to 83% in studies of small groups. Among children followed for more than two years, 44% saw their cyst disappear with observation alone, and younger children (under 10) had better odds of spontaneous resolution than older ones.
Skin cysts, on the other hand, rarely resolve by themselves. They may shrink temporarily but tend to persist or recur unless the entire sac wall is removed.
When Treatment Is Needed
Most cysts don’t need treatment unless they’re causing symptoms. A cyst that’s painful, infected, growing, or pressing on nearby structures is a candidate for removal. For ovarian dermoid cysts, the risk of a serious complication called torsion (where the cyst’s weight causes the ovary to twist on itself, cutting off blood flow) increases once the cyst exceeds 5 to 6 cm. Emergency surgery is required if torsion occurs.
Smaller cysts that do need removal can often be handled with minimally invasive surgery, which means shorter recovery times and smaller incisions. Cysts above 10 cm generally require a larger surgical approach. In a study of ovarian dermoid cysts, those larger than 12 cm were significantly more likely to need open surgery rather than the minimally invasive alternative. For skin cysts, a minor in-office procedure to excise the sac is the standard approach and typically takes less than 30 minutes.
Drainage alone, where a needle is used to draw fluid out of the cyst, provides temporary relief but has a high recurrence rate because the sac wall remains intact and refills over time.
Warning Signs of a Ruptured Cyst
Internal cysts, particularly ovarian cysts, can rupture. When this happens, you may feel sudden, sharp pain in your lower abdomen or back, along with vaginal spotting or bloating. Many ruptured cysts cause temporary discomfort that resolves as the fluid is absorbed by the body.
However, some ruptures are more serious. Seek emergency care if you experience severe nausea and vomiting (which can signal torsion), fever (suggesting infection), heavy vaginal bleeding, or faintness and dizziness (which may indicate internal bleeding). Torsion in particular requires prompt surgery to restore blood flow to the ovary and prevent permanent damage.