Most ovarian cysts form as a normal byproduct of the menstrual cycle, when the fluid-filled sac that releases an egg each month either fails to open or fails to shrink afterward. These so-called functional cysts are overwhelmingly the most common type and usually disappear on their own within a few weeks. But “ovarian cyst” is a broad label that covers everything from harmless, self-resolving bubbles of fluid to endometriomas packed with old blood, dermoid cysts containing bits of tissue like hair and teeth, and cysts triggered by pregnancy hormones, medications, or thyroid disorders. The causes, risk factors, and clinical significance vary enormously depending on which type you are dealing with.
Functional Cysts and the Normal Menstrual Cycle
Every month, one of your ovaries develops a small fluid-filled structure called a follicle, which houses the maturing egg. At mid-cycle, that follicle is supposed to rupture, release the egg, and then collapse into a temporary hormone-producing structure called the corpus luteum. A functional cyst forms when something in this sequence goes slightly off-script.
A follicular cyst appears when the follicle doesn’t rupture at ovulation. The egg may be released, but the sac keeps growing and filling with fluid instead of deflating. These cysts are usually painless, show up incidentally on an ultrasound, and resolve within one to three menstrual cycles without treatment.
A corpus luteum cyst forms on the other side of ovulation. After the egg leaves, the empty follicle normally shrinks. Sometimes, instead of collapsing, it seals itself shut and fluid or blood accumulates inside. A hemorrhagic corpus luteum cyst is a version where spontaneous bleeding fills the structure after ovulation.1PubMed Central. Hemorrhagic corpus luteum: Clinical management update These can cause a sharp, one-sided pelvic pain that sends people to the emergency room, but they too tend to resolve on their own.
The key thing about both types is that they are not a disease. They are minor hiccups in an otherwise normal process. If you are cycling regularly, you will almost certainly develop functional cysts at some point, even if you never notice them.
Endometriomas
Endometriomas are a different animal. Sometimes called “chocolate cysts” because of the dark, old blood they contain, they form in people with endometriosis. The leading theory is that endometrial-like tissue invades the ovary or that existing functional cysts undergo a transformation, with endometriotic tissue bleeding repeatedly into the ovarian cortex and creating a thick-walled, blood-filled cavity.2PubMed Central. Pathophysiology and Clinical Implications of Ovarian Endometriomas Unlike functional cysts, endometriomas do not go away on their own. They can grow over time, cause significant pain, and damage surrounding ovarian tissue, which is one reason they are a concern for fertility.
If you have been diagnosed with endometriosis, the presence of an endometrioma is not surprising, but it does change the clinical conversation. These cysts are more likely to recur after surgical removal and may require long-term hormonal management to keep them in check.
Dermoid Cysts and Other Germ Cell Tumors
Dermoid cysts, formally called mature cystic teratomas, are among the stranger things the body can produce. They arise from germ cells, the same cells that would ordinarily become eggs, and can contain tissue types you’d expect to find elsewhere in the body: skin, hair follicles, sebaceous glands, and occasionally bone or teeth. They are benign in the vast majority of cases, grow slowly, and are often found incidentally during imaging for something else.
A prospective study tracking dermoid cysts in premenopausal women found an average growth rate of about 1.8 mm per year, while in postmenopausal women the cysts actually shrank slightly over time.3PubMed. The growth pattern of ovarian dermoid cysts: a prospective study in premenopausal and postmenopausal women That glacial pace is why many clinicians opt for monitoring rather than immediate surgery, especially for smaller cysts. The concern with dermoids is less about what they are and more about their size: a larger dermoid increases the risk of ovarian torsion, where the ovary twists on its blood supply.
Cysts Triggered by Pregnancy
Pregnancy introduces a hormone that can push ovarian tissue into overdrive: human chorionic gonadotropin, or hCG. In some pregnancies, high hCG levels or an unusual sensitivity to the hormone cause the ovaries to develop theca lutein cysts, which are often large, bilateral, and multilocular (containing multiple fluid-filled compartments).4PubMed Central. Rupture of Bilateral Theca Lutein Cysts During Pregnancy: A Case Report
Theca lutein cysts are particularly associated with conditions where hCG levels run especially high, including twin or triplet pregnancies, gestational trophoblastic disease (molar pregnancies), and pregnancies following fertility treatment.5PubMed Central. Theca lutein cysts and early onset severe preeclampsia In up to about 30% of affected patients, theca lutein cysts produce enough androgens to cause visible signs like excess hair growth or acne.6PubMed Central. Delayed postpartum regression of theca lutein cysts with maternal virilization: A case report The reassuring part is that these cysts almost always resolve after the pregnancy ends and hCG levels drop, though that regression can sometimes take weeks to months postpartum.
Fertility Medications and Iatrogenic Cysts
Medications used to induce ovulation are a well-known trigger for ovarian cysts. Clomiphene citrate, one of the most commonly prescribed fertility drugs, works by stimulating the ovaries to produce more follicles. Sometimes those stimulated follicles persist rather than ovulating and collapsing. In a study of over 3,200 women taking clomiphene for ovulation induction, 186 developed cysts larger than 20 mm on the third day of the following cycle.7PubMed. Treatment of clomiphene citrate-related ovarian cysts in a prospective randomized study. A single center experience That works out to roughly 6% of treated cycles, frequent enough that clinicians routinely check with ultrasound before starting the next round of medication.
Injectable gonadotropins used in IVF carry even higher rates of ovarian hyperstimulation, which can produce multiple large cysts along with fluid shifts that affect the whole body. The takeaway for anyone undergoing fertility treatment is that cyst formation is not a complication in the alarming sense; it is a recognized side effect of deliberately pushing the ovaries to do more than they ordinarily would. It does, however, require monitoring to avoid the more serious consequences of overstimulation.
Thyroid Disorders and Hormonal Crosstalk
An underactive thyroid gland can lead to ovarian cysts through a less obvious hormonal pathway. When the thyroid is severely underperforming, the pituitary gland ramps up production of thyroid-stimulating hormone (TSH). Because TSH shares structural similarity with the hormones that stimulate the ovaries, very high TSH levels can cross-react with ovarian tissue and trigger cyst formation. A case series described patients with severe hypothyroidism who developed ovarian masses large enough to mimic malignancy. After starting thyroid replacement therapy, the cysts resolved completely on follow-up imaging.8PubMed Central. Hypothyroidism Presenting as Ovarian Cysts-a Case Series
This is worth knowing because it means not every ovarian cyst requires a gynecological solution. If you have unexplained ovarian cysts alongside symptoms of hypothyroidism, such as fatigue, weight gain, cold intolerance, and irregular periods, checking thyroid function could save you from unnecessary surgery.
Body Composition, Obesity, and Environmental Exposures
Body fat distribution appears to influence the risk of several reproductive conditions, including polycystic ovary syndrome. A large genetic study using Mendelian randomization found that a higher waist-to-hip ratio, a marker of central fat accumulation, was linked to increased risk of PCOS, and that the estimated amount of visceral abdominal fat was independently associated with PCOS as well.9PLOS Medicine. Obesity and risk of female reproductive conditions: A Mendelian randomisation study The same study found genetic links between central obesity and endometriosis. Because PCOS and endometriosis are both major drivers of pathological ovarian cysts, the connection between body composition and cyst development runs through these conditions rather than being a direct cause-and-effect on the ovary itself.
Environmental chemicals add another layer. Endocrine-disrupting compounds like bisphenol A (BPA) and phthalates, found in plastics, food packaging, and personal care products, can interfere with the body’s hormonal signaling. Research suggests that prenatal exposure to these chemicals may contribute to altered reproductive programming and could increase susceptibility to PCOS later in life, and that ongoing exposure in adulthood can destabilize hormonal balance in ways that affect ovarian function.10PubMed. Polycystic ovary syndrome and environmental toxins The evidence is still evolving, and no one can draw a straight line from a particular plastic container to a particular cyst. But the general finding that hormone-mimicking chemicals affect reproductive health is well established enough that it belongs in any honest accounting of risk factors.
How Age and Menopause Change the Picture
Ovarian cysts are overwhelmingly a premenopausal phenomenon, for the simple reason that most cysts arise from the menstrual cycle and the hormonal fluctuations that drive it. Once ovulation stops at menopause, the most common cause of new cyst formation goes away. But cysts don’t disappear entirely after menopause. A study following 134 postmenopausal women with incidentally discovered ovarian cysts found that in about 29% of women, the cysts eventually disappeared, while in roughly half the cysts persisted unchanged, and in 13%, new cysts developed during the follow-up period.11Wiley Online Library (Ultrasound in Obstetrics & Gynecology). The natural history of adnexal cysts incidentally detected at transvaginal ultrasound examination in postmenopausal women
The clinical significance of a cyst shifts with age. In a premenopausal woman, a simple-looking cyst on ultrasound is almost always benign. After menopause, the index of suspicion rises. One study found that about 38% of ovarian masses in a postmenopausal group were malignant, compared with roughly 8% in a premenopausal group.12Asian Pacific Journal of Cancer Prevention. Predictive Value of Malignancy Risk Indices for Ovarian Masses in Premenopausal and Postmenopausal Women That does not mean a postmenopausal cyst is likely to be cancer, since most still turn out to be benign. But it does mean that a new or growing cyst after menopause warrants closer follow-up and possibly additional testing, whereas the same cyst in a 28-year-old would typically be watched with a repeat ultrasound.
When Cysts Become Emergencies
Most ovarian cysts cause no symptoms and need no treatment. The exceptions are torsion and rupture, both of which can become surgical emergencies.
Ovarian torsion occurs when a cyst makes the ovary heavy or mobile enough to twist on its stalk, cutting off blood flow. A study modeling torsion risk found that cysts between 5 and 10 cm in diameter, cysts on the right side, multilocular cysts, and cysts with thicker walls all independently increased the odds of torsion.13PubMed Central. Construction of a risk prediction model for ovarian cyst pedicle torsion based on multimodal ultrasound parameter characteristics and an analysis of its clinical application value The right-side predominance is thought to relate to the sigmoid colon on the left side limiting the ovary’s range of movement. Torsion presents as sudden, severe, one-sided pelvic pain, often with nausea and vomiting, and requires emergency surgery to untwist the ovary before the tissue dies.
Ruptured cysts are more common and usually less dire. A small functional cyst that pops may cause a brief stab of pain and nothing more. But when a hemorrhagic cyst ruptures, bleeding can spill into the abdominal cavity. In severe cases, the resulting hemoperitoneum, blood pooling in the abdomen, can lead to drops in blood pressure and even hypovolemic shock if not caught quickly.14PubMed Central. A Case of Hemorrhagic Ovarian Cyst Rupture Necessitating Surgical Intervention If you experience sudden pelvic pain with dizziness, lightheadedness, or fainting, that combination warrants emergency evaluation.
Can Oral Contraceptives Prevent Cysts?
Oral contraceptive pills suppress ovulation, which should in theory eliminate the main pathway for functional cyst formation. The evidence broadly supports this, but with a nuance that often gets lost. Combined oral contraceptives are effective at preventing new functional cysts from forming because they stop the follicle-development process. They are less reliable at shrinking cysts that already exist, which is why “just go on the pill” is not always a satisfying answer when you already have a symptomatic cyst.
Beyond functional cysts, longer-term contraceptive use appears to affect a different type of ovarian cyst entirely. Research found that using oral contraceptives for more than five years significantly reduced the development of cortical inclusion cysts, tiny invaginations of the ovarian surface epithelium that are considered a possible precursor to certain ovarian cancers.15PubMed Central. Impact and mechanistic role of oral contraceptive pills on the number and epithelial type of ovarian cortical inclusion cysts; a clinicopathology and immunohistochemical study This finding is part of the broader body of evidence linking long-term oral contraceptive use to reduced ovarian cancer risk, one of the clearest protective effects of the pill.
What “Incidental” Cysts Mean on an Imaging Report
With the widespread use of pelvic ultrasound for everything from fertility workups to investigating unrelated abdominal symptoms, ovarian cysts show up on imaging all the time in people who had no idea they were there. These incidental findings can trigger real anxiety, but the natural history data is reassuring. In the postmenopausal follow-up study mentioned earlier, the vast majority of incidentally detected cysts either stayed the same size or resolved entirely, and none of the benign-appearing simple cysts in that cohort turned out to be malignant.11Wiley Online Library (Ultrasound in Obstetrics & Gynecology). The natural history of adnexal cysts incidentally detected at transvaginal ultrasound examination in postmenopausal women
If you are premenopausal and an ultrasound shows a simple, thin-walled cyst under 5 cm with no solid components, the standard approach is to recheck in six to eight weeks. Most will have vanished by then. Features that make a cyst worth investigating further include solid areas within the cyst, thick internal walls or septations, evidence of blood flow inside the solid parts, and the presence of free fluid in the pelvis suggesting rupture. These features don’t confirm malignancy, but they do push the probability high enough that further testing, such as tumor markers or MRI, is warranted.
The broader point is that the word “cyst” on an imaging report carries very different weight depending on context. A 3 cm simple cyst in a 30-year-old is almost certainly a functional cyst that will resolve without anyone lifting a finger. A complex 8 cm cyst in a 65-year-old with a rising CA-125 level is an entirely different clinical scenario. Knowing which category you fall into matters far more than the word “cyst” by itself.