An ovarian cyst is a fluid-filled sac that forms in or on an ovary, usually as a normal part of the menstrual cycle. Most ovarian cysts are harmless, cause no symptoms, and disappear on their own within two to three menstrual cycles. Roughly 20% of women develop at least one ovarian or pelvic mass during their lifetime, and the vast majority turn out to be benign.
How Ovarian Cysts Form
Each month, your ovaries grow a small fluid-filled follicle that houses a maturing egg. When hormones signal ovulation, the follicle ruptures, releases the egg, and then shrinks into a temporary structure called the corpus luteum, which produces progesterone to support a potential pregnancy. This process is completely normal and happens every cycle.
A cyst forms when something in that sequence doesn’t go as planned. If the follicle never ruptures, it keeps growing and fills with fluid, becoming a follicular cyst. If the follicle does release its egg but the opening seals shut afterward, fluid accumulates inside the corpus luteum, creating a corpus luteum cyst. These two types are called functional cysts because they arise from the ovary’s normal function. They’re the most common kind, and getting one actually signals that your reproductive system is working as it should.
Types Beyond Functional Cysts
Not all ovarian cysts are tied to the menstrual cycle. Several other types develop through different mechanisms and tend to stick around longer.
- Dermoid cysts grow from the cells that produce eggs (germ cells) and can contain surprisingly varied tissue, including fat, hair, and even teeth-like material. They’re benign in the vast majority of cases but don’t resolve on their own.
- Endometriomas form when tissue similar to the uterine lining grows on or inside the ovary. They fill with old, dark blood, which is why they’re sometimes called “chocolate cysts.” They’re closely linked to endometriosis.
- Cystadenomas develop from cells on the ovary’s surface. Serous cystadenomas contain thin, watery fluid, while mucinous cystadenomas hold thicker, gel-like fluid and often have multiple compartments. Both are typically benign.
- Polycystic ovaries look different from a single large cyst. In polycystic ovary syndrome (PCOS), excess androgen hormones cause the ovaries to develop many small follicular cysts and enlarge over time.
What Ovarian Cysts Feel Like
Most ovarian cysts produce no symptoms at all. They’re frequently discovered by accident during an ultrasound done for another reason. When a cyst does cause symptoms, the most common one is a dull ache or sense of pressure on one side of the lower abdomen. You might also notice bloating, a feeling of fullness, or pain during sex. Some cysts can cause irregular periods or spotting between cycles, particularly corpus luteum cysts that affect progesterone levels.
Larger cysts are more likely to produce noticeable discomfort simply because they take up more space and can press on the bladder or bowel. A cyst over 5 to 6 centimeters increases the risk of complications like torsion, which is when the weight of the cyst causes the ovary to twist on itself.
When a Cyst Becomes an Emergency
Two complications require immediate medical attention: rupture and torsion.
A ruptured cyst releases its fluid into the pelvic cavity, which can cause sudden, sharp pain on one side of the lower abdomen. In most cases the pain is intense but short-lived, and the body reabsorbs the fluid. Occasionally, if a blood vessel tears during the rupture, internal bleeding can become serious enough to need treatment.
Ovarian torsion is more dangerous. The pain is typically sudden and severe, often described as sharp and stabbing, and it usually comes with nausea and vomiting. The pain tends to be constant and can radiate to the thighs, sides, or lower back. Because torsion cuts off blood flow to the ovary, the tissue can start to die. Signs of that progression include fever and abnormal vaginal bleeding or discharge. If you have unexplained, severe lower abdominal pain, especially if you know you have a cyst, go to the emergency room. A transvaginal ultrasound can quickly confirm or rule out torsion by checking whether blood is still flowing to the ovary.
How Cysts Are Diagnosed
Ultrasound is the primary tool for identifying and classifying ovarian cysts. A transvaginal ultrasound gives the clearest picture and lets a clinician determine whether the cyst is simple (a single thin-walled sac filled with clear fluid) or complex (containing solid areas, internal walls dividing it into compartments, or irregular features). Simple cysts are overwhelmingly benign. Complex cysts sometimes need further evaluation, but most still turn out to be noncancerous.
For postmenopausal women, who often worry most about ovarian cancer, the data is reassuring. A large meta-analysis found that simple ovarian cysts in postmenopausal women became cancerous at a rate of roughly 1 in 10,000. Most either stayed the same size or disappeared entirely over time.
Treatment and Size Thresholds
Functional cysts under 5 centimeters rarely need any treatment. The standard approach is to simply wait and repeat the ultrasound after one or two cycles to confirm the cyst has shrunk or resolved. Many women are told they have a cyst and never hear about it again because it’s gone by the next scan.
Cysts larger than 5 to 6 centimeters get closer attention because the risk of torsion increases at that size. If a cyst persists, keeps growing, or causes significant symptoms, surgical removal may be recommended. Cysts above 10 centimeters generally call for surgery. For cysts in the 5 to 10 centimeter range, the decision often depends on the type of cyst, your symptoms, your age, and what the ultrasound looks like. Complex features, solid components, or signs of blood flow within the cyst wall raise the level of concern and may push toward removal even at smaller sizes.
For dermoid cysts specifically, the risk of a rare cancerous transformation increases with age over 45, cyst diameter over 10 centimeters, and rapid growth. These factors typically prompt more proactive surgical planning.
Effects on Fertility
Functional cysts do not cause infertility. Getting one is actually evidence that ovulation is happening normally, which is the key biological event needed for conception. These cysts resolve on their own and don’t damage the ovary.
Endometriomas are different. Because they’re tied to endometriosis, a condition that can cause inflammation, scarring, and adhesions throughout the pelvis, they are associated with reduced fertility. The cyst itself, combined with the broader effects of endometriosis on the reproductive organs, can make conception more difficult. Treatment for endometriomas, whether surgical or through assisted reproduction, depends on the size, severity, and your plans for pregnancy.
PCOS affects fertility through a different pathway. The many small cysts on the ovaries reflect a hormonal imbalance that disrupts regular ovulation. Without consistent ovulation, the chances of conceiving each month drop. PCOS is one of the most common causes of ovulatory infertility, but it responds well to treatment in many cases.