Most ovarian cysts are not dangerous. The majority are functional cysts, meaning they form as a normal part of your menstrual cycle, cause no symptoms, and disappear on their own within a few weeks. In premenopausal women, not a single simple cyst was found to be cancerous in a large ultrasound study of over 50,000 women published in JAMA Internal Medicine. That said, certain types of cysts do carry real risks, and knowing the difference matters.
Why Most Cysts Are Harmless
Every month, your ovaries grow small fluid-filled sacs called follicles. When a follicle doesn’t release its egg or doesn’t dissolve afterward as it should, it can linger as a cyst. These functional cysts fall into two categories: follicular cysts (from an unreleased egg) and corpus luteal cysts (from a sac that doesn’t break down after ovulation). Both are extremely common, generally painless, and resolve without treatment.
Corpus luteal cysts are also present during early pregnancy and typically disappear by the end of the first trimester. Simple cysts smaller than 5 centimeters in premenopausal women don’t even require follow-up imaging, according to current NHS clinical guidelines. They’re considered so low-risk that doctors can safely discharge you without monitoring.
Types That Need Closer Attention
Not all cysts are functional. Some arise from abnormal cell growth or other conditions, and these don’t resolve on their own. The key distinction: if a cyst persists through several menstrual cycles, it’s unlikely to be a simple functional cyst and warrants further evaluation.
Dermoid cysts are growths that can contain tissue like hair, skin, or even teeth, because they develop from the same type of cells that form different body tissues. They’re almost always benign but can grow large enough to twist the ovary (more on that below). Cysts larger than 5 to 6 centimeters carry a meaningful risk of this complication.
Endometriomas (sometimes called chocolate cysts) form when tissue similar to the uterine lining grows on or inside an ovary. Having endometriomas signals moderate to severe endometriosis. They can cause scar tissue and inflammation around the ovaries and fallopian tubes, potentially leading to fertility problems. They also carry a small increased risk of ovarian cancer, though this remains rare. Removing endometriomas can improve symptoms and reduce the chance of rupture or infertility.
When a Cyst Becomes an Emergency
The two acute complications worth knowing about are rupture and torsion. Both cause sudden, severe pelvic pain and can require emergency treatment.
Ruptured Cysts
When a cyst bursts, it can leak fluid or blood into your abdomen. Many ruptured cysts cause a sharp jolt of pain that fades on its own. But some cause significant internal bleeding. In a study of women with ruptured cysts and bleeding, about 6.5% of those with stable vital signs and minimal fluid needed surgery, while nearly 78% of those with low blood pressure and a large amount of internal fluid required an operation.
The pain from a rupture often mimics appendicitis, especially since cysts are more common on the right side. Symptoms that signal a true emergency include nausea or vomiting (leaked cyst contents can make you very sick), fever (a sign of possible infection), and dizziness or a racing heartbeat (signs of significant blood loss). If you experience any of these alongside intense abdominal pain, get medical attention immediately.
Ovarian Torsion
Torsion happens when a cyst makes the ovary heavy enough to twist on the ligaments that hold it in place. This twist cuts off blood flow, first blocking drainage from the ovary and then, as swelling increases, blocking the blood supply going in. Without treatment, the ovary can die. The main risk factor is a cyst 5 centimeters or larger. Torsion causes sudden, intense pain, often with nausea, and requires emergency surgery to untwist the ovary and save it.
How Doctors Tell Benign From Concerning
Ultrasound is the primary tool for evaluating ovarian cysts, and experienced examiners are highly effective at distinguishing benign from potentially malignant growths based on what the cyst looks like inside. Simple cysts appear as smooth, thin-walled, fluid-filled structures. These are almost universally benign.
Features that raise concern include thick internal walls dividing the cyst into chambers, solid areas with blood flow, and finger-like projections growing from the cyst wall. Endometriomas can sometimes mimic a cyst with solid components because of the debris inside them, and in postmenopausal women, any atypical-looking endometrioma needs careful evaluation because the risk of malignancy is higher in that age group.
Your doctor may also order a blood test for a protein called CA-125, which can be elevated with ovarian cancer but also rises with endometriosis, fibroids, and even normal menstruation. It’s most useful in postmenopausal women, where the results are less likely to be muddied by other conditions.
The Cancer Question
This is usually what people really want to know, and the numbers are reassuring. Among premenopausal women with simple cysts on ultrasound, zero cases of cancer were found in the JAMA Internal Medicine study. Among postmenopausal women with simple cysts, just 1 out of 2,347 was later diagnosed as cancer, a rate of roughly 0.04%.
Cancer risk rises with age, complex ultrasound features, and a family history of ovarian or breast cancer. A simple, fluid-filled cyst in a 30-year-old is an entirely different situation from a complex, multi-chambered mass with blood flow in a 65-year-old. Doctors use this context, not cyst presence alone, to assess your risk.
Monitoring and Size Thresholds
How a cyst gets managed depends mostly on its size, appearance, and whether you’ve gone through menopause.
For premenopausal women, simple cysts under 5 centimeters need no follow-up at all. Cysts between 5 and 7 centimeters get a repeat ultrasound in three months. If the cyst resolves, you’re done. If it’s unchanged, another scan happens at one year. Beyond that, ongoing surveillance is individualized based on your risk factors.
For postmenopausal women, the thresholds are more conservative. Simple cysts under 1 centimeter need no monitoring. Cysts between 1 and 5 centimeters are rechecked with ultrasound and blood work every four to six months for a year. If nothing changes, you can be reassured and discharged.
Surgery typically enters the conversation when cysts are larger than 5 to 6 centimeters (because of torsion risk), when they have concerning features on ultrasound, or when they cause persistent symptoms. Cysts above 10 centimeters generally need surgical removal, and very large cysts over 12 centimeters often require a traditional open incision rather than a minimally invasive approach.
Cysts and Fertility
Functional cysts don’t affect your ability to get pregnant. In fact, corpus luteal cysts are a normal part of early pregnancy. The cysts that can threaten fertility are endometriomas, which cause scarring and inflammation that may block or damage the fallopian tubes. If you’re trying to conceive and have been diagnosed with endometriomas, removing them can improve your chances, though surgery itself can slightly reduce the egg supply in the affected ovary. This is a tradeoff worth discussing with a specialist who can weigh your specific situation.