An ovarian cyst is a fluid-filled sac that forms on or inside an ovary. They are extremely common, affecting roughly 7% of women worldwide at any given time, and most resolve on their own without treatment. In the vast majority of cases, ovarian cysts are harmless and painless, often discovered by accident during a routine pelvic exam or ultrasound for something else entirely.
How Ovarian Cysts Form
The most common ovarian cysts are called functional cysts because they arise from the normal work your ovaries do each month. During a typical menstrual cycle, an egg grows inside a small fluid-filled sac called a follicle. When the follicle doesn’t release the egg as expected, or doesn’t shrink afterward, it can keep growing and become a cyst. There are two main types.
A follicular cyst forms when the follicle holding the egg doesn’t open to release it. These are filled with clear fluid, have very little blood supply, and tend to be the least troublesome. A corpus luteum cyst forms after ovulation, when the empty follicle that released the egg seals itself off and fills with fluid instead of shrinking. Corpus luteum cysts are more metabolically active because they produce progesterone, and they have a rich blood supply, which is why they sometimes bleed internally if they rupture.
Both types typically disappear within one to three menstrual cycles without any intervention.
Other Types of Ovarian Cysts
Less commonly, cysts develop from abnormal cell growth rather than from the normal menstrual cycle. These are sometimes called nonfunctional or pathological cysts. Any of the tissue types inside an ovary can grow into a cyst, which is why they come in several varieties: some are filled with mucus, some with watery fluid, and some (called dermoid cysts) can contain surprising materials like hair, skin cells, or even teeth, because they grow from the cells that produce eggs.
Endometriomas are another type. These form when tissue similar to the uterine lining grows on the ovary, creating cysts filled with old blood. They’re sometimes called “chocolate cysts” because of their dark brown appearance and are closely linked to endometriosis.
A small number of nonfunctional cysts turn out to be ovarian cancer. This is uncommon, but it’s the reason providers pay close attention to cysts that look complex on ultrasound, meaning they have solid areas, internal walls, or nodular projections rather than being simple, smooth, fluid-filled sacs.
Symptoms to Recognize
Most ovarian cysts produce no symptoms at all. When they do, it’s usually because the cyst has grown large enough to press on surrounding tissue or has started to leak or bleed. The most common symptom is pelvic pain, typically a dull ache on one side of your lower belly. You might also notice:
- Bloating or fullness in your lower abdomen, often more pronounced on one side
- Pain during sex
- Irregular or painful periods
- Pressure on your bladder or bowel, causing frequent urination or difficulty with bowel movements
- A dull ache in your lower back
These symptoms overlap with many other conditions, which is why imaging is usually needed to confirm that a cyst is the cause.
When a Cyst Becomes an Emergency
Two complications require immediate medical attention: rupture and torsion.
A ruptured cyst causes sudden, sharp pain in the pelvis, usually intense and located to one side. Nausea, vomiting, and vaginal bleeding can follow. Most ruptured cysts resolve with pain management alone, but corpus luteum cysts can bleed significantly because of their rich blood supply, occasionally requiring emergency treatment.
Ovarian torsion happens when a cyst makes the ovary heavy enough to twist on its own blood supply, cutting off circulation. The hallmark is sudden, severe lower abdominal pain, often accompanied by nausea and vomiting. The pain can feel sharp and stabbing or dull and crampy, and it may radiate to your thighs, sides, or lower back. Torsion is a surgical emergency. If blood flow isn’t restored quickly, the ovarian tissue begins to die, which can lead to fever, abnormal discharge, and in rare cases a serious abdominal infection. If you know you have an ovarian cyst and develop sudden, unexplained pelvic pain, get to an emergency room.
How Ovarian Cysts Are Diagnosed
Ovarian cysts are most often found during a pelvic ultrasound. The ultrasound shows the cyst’s location, its size, and whether it’s filled with fluid (simple) or contains solid areas (complex). That distinction matters because simple cysts are almost always benign, while complex cysts need closer evaluation.
A simple cyst on ultrasound has five features: a round or oval shape, a thin wall, clear fluid with no internal structures, no solid nodules, and no internal dividing walls. If any of those features are absent, the cyst is classified as complex.
When a cyst looks suspicious or you have risk factors for ovarian cancer, your provider may order a blood test measuring a protein called CA-125. Elevated levels can indicate ovarian cancer, but they also rise with noncancerous conditions like endometriosis and pelvic inflammatory disease, so the test is used alongside imaging rather than on its own. In some cases, a small camera inserted through a tiny abdominal incision (laparoscopy) is used to get a direct look at the ovary.
Treatment and Monitoring
The approach depends entirely on the cyst’s size, appearance, and whether it’s causing symptoms.
Small, simple cysts under 3 centimeters (about 1.2 inches) in diameter have a very low risk of being anything concerning and generally don’t need follow-up at all. Simple cysts between 3 and 5 centimeters are typically monitored with a repeat ultrasound in four to six months. If the cyst stays the same size or shrinks over the course of a year, and blood work remains normal, routine monitoring can usually stop.
Functional cysts in premenopausal women often just need time. Your provider may recommend a “watch and wait” approach, rechecking with ultrasound after one to three cycles to confirm the cyst is resolving. Pain relievers can help manage discomfort in the meantime.
Surgery becomes the recommendation when a cyst is large, complex, persistent, or causing significant symptoms. A complex cyst with solid components, internal walls, or nodular projections needs surgical evaluation to rule out cancer. The procedure is often done laparoscopically through small incisions, and in many cases the cyst can be removed while preserving the ovary.
Can You Prevent Ovarian Cysts?
Hormonal birth control reduces the chance of developing new functional cysts by suppressing ovulation. Research shows women using hormonal contraception have significantly fewer ovarian cysts: one study found the incidence dropped from 9.5% in women not using contraception to 2.4% in those on hormonal birth control for at least three months. That said, hormonal contraception won’t make an existing cyst go away faster. It prevents new ones from forming rather than treating ones already there.
There’s no reliable way to prevent nonfunctional cysts like dermoid cysts or endometriomas, since these grow from abnormal tissue rather than from the ovulation process.