Ovarian cysts are extremely common. Most women will develop at least one during their reproductive years, and the majority form and resolve without ever being noticed. Functional cysts, the kind that develop as a normal part of ovulation each month, are so routine that finding one on an ultrasound is often no more remarkable than finding food in your stomach.
Why Most Cysts Are Part of Normal Biology
Every menstrual cycle, an ovary grows a small fluid-filled sac called a follicle. This follicle holds a developing egg and typically reaches about 2 to 3 centimeters before releasing it at ovulation. Sometimes the follicle doesn’t release the egg and keeps growing, forming what’s called a follicular cyst. Other times, the sac that remains after ovulation fills with fluid instead of breaking down, creating a corpus luteum cyst. Both are classified as functional cysts, and both almost always disappear on their own within one to three menstrual cycles.
These functional cysts are rarely larger than 7 centimeters and represent the vast majority of cysts found in premenopausal women. Because the ovary is constantly cycling through egg development and ovulation, finding a cyst on any given ultrasound is expected rather than unusual. This is why doctors typically treat a simple cyst in a younger woman as a normal finding rather than a problem.
How Often Cysts Show Up on Imaging
The widespread use of ultrasound, CT scans, and MRIs for unrelated health concerns has dramatically increased how often ovarian cysts are discovered by accident. A woman getting a scan for back pain, a kidney issue, or a pregnancy checkup may learn she has a cyst she never felt. During pregnancy alone, incidental ovarian cysts are found in 1% to 6% of women scanned.
Even after menopause, when the ovaries are far less active, cysts remain surprisingly common. A large cancer screening study that followed over 15,000 women older than 55 found that 14% had a simple ovarian cyst the first time their ovaries were visualized on ultrasound. Each year, about 8% of the women developed a new cyst. Yet roughly a third of the cysts found at the start of the study had disappeared entirely by the one-year follow-up, and the risk of any of these simple cysts being cancerous was close to zero.
Types Beyond Functional Cysts
Not every ovarian cyst is tied to the menstrual cycle. Some develop from other tissue types and stick around longer.
- Dermoid cysts (also called mature cystic teratomas) are the most common type of ovarian tumor, making up 10% to 25% of all ovarian tumors and nearly 60% of benign ovarian growths across all age groups. They form from cells present since birth and can contain unexpected tissue like hair, skin, or even teeth. They grow slowly and are almost always noncancerous, but they don’t resolve on their own.
- Endometriomas develop when tissue similar to the uterine lining grows on or inside the ovary. Sometimes called “chocolate cysts” because of the dark blood they contain, these are closely linked to endometriosis and can cause significant pain.
- Cystadenomas form on the outer surface of the ovary and are filled with watery or mucus-like fluid. They can grow quite large but are typically benign.
Polycystic ovary syndrome (PCOS) is a separate condition that affects an estimated 10% to 13% of women of reproductive age. Despite the name, having polycystic-appearing ovaries on ultrasound is just one possible feature of the syndrome, and many women with PCOS don’t actually have ovarian cysts. The small “cysts” seen in PCOS are really immature follicles that haven’t completed development, not the fluid-filled sacs most people picture.
When a Cyst Causes Problems
Most cysts produce no symptoms at all. When they do, the most common sign is a dull ache or pressure on one side of the lower abdomen, sometimes noticeable during certain points in the menstrual cycle. Larger cysts can cause bloating or a feeling of fullness.
The more serious complications are rupture and torsion. A ruptured cyst can cause sudden, sharp pain and sometimes internal bleeding, though many ruptures cause only brief discomfort and resolve without treatment. Ovarian torsion, where the weight of a cyst causes the ovary to twist on its blood supply, occurs in roughly 10% of ovarian cyst cases and is a gynecological emergency. Torsion causes intense, sudden pain often accompanied by nausea and requires prompt surgical treatment to save the ovary.
How Doctors Decide What Needs Follow-Up
The size, appearance, and your age all factor into whether a cyst warrants monitoring or can be safely ignored. Guidelines from the American College of Obstetricians and Gynecologists (ACOG) state that simple cysts up to 10 centimeters are likely benign and can be monitored with repeat imaging rather than surgery, even in postmenopausal women.
For women still in their reproductive years, the American College of Radiology recommends no follow-up imaging at all for simple cysts smaller than 5 centimeters found incidentally on a high-quality ultrasound. These are considered normal. For postmenopausal women, cysts smaller than 1 centimeter also need no follow-up. Simple cysts between 1 and 5 centimeters in postmenopausal women are typically rechecked with ultrasound in 4 to 6 months.
What makes a cyst look more concerning on imaging isn’t necessarily its size but its internal characteristics. Cysts with solid components, thick internal walls, irregular borders, or blood flow within the walls get closer scrutiny. A purely fluid-filled, thin-walled cyst is almost always benign regardless of when in life it appears.
Cancer Risk in Context
One of the main reasons people search for how common ovarian cysts are is worry about cancer. The reassuring reality is that the overwhelming majority of ovarian cysts, at any age, are not cancerous. In premenopausal women, most cyst findings are directly related to normal ovulation and resolve without any intervention.
Risk does shift somewhat after menopause, because the ovaries are no longer cycling and any new growth deserves a closer look. But even in the large screening study of women over 55, simple cysts carried a near-nonexistent cancer risk. The cysts that raise concern are complex ones with solid areas or other irregular features, not the smooth, fluid-filled type most commonly found. Age, family history, and imaging characteristics together help determine whether a cyst needs biopsy or surgical removal rather than watchful waiting.