The Most Common Causes of Ovarian Cysts

While the vagina gets a lot of attention for serving as the birth canal (and primary sex organ for some people), it's only one part of an entire reproductive system made of many different organs and body parts

One of those organs—which technically comes as a pair—is the body's ovaries. These are small, oval-shaped glands located on either side of the uterus, usually next to the fimbriated end (the end of the fallopian tube with finger-like structures). Ovaries typically produce eggs and hormones, play an important role in your menstrual cycle each month, and are the starting point for possible conception.

But, as helpful as the ovaries are, they can also develop cysts, or noncancerous growths that can form inside or on the surface of the ovary. Though most cysts don't cause any discomfort and often go away on their own, sometimes cysts can cause abdominal pressure, bloating, swelling, and pain in the lower abdomen, on the side of the ovary with the cyst, according to the Office on Women's Health. More severe symptoms can include sharp pain with nausea and vomiting, which is a sign that you need emergency medical attention.

There are a few different causes of ovarian cysts (and, because of that, different types of ovarian cysts)—here's what you need to know about each one.

Your Menstrual Cycle

Functional cysts—aka follicular cysts and corpus luteum cysts—form at different parts of the menstrual cycle and usually go away on their own. The follicle is a clear sac of fluid containing the egg as it prepares to be released during ovulation, according to the Office on Women's Health.

"There are times where you could have a follicle that grows and grows and grows, and doesn't necessarily release an egg, and that's what we would call a follicular cyst," Rebecca Brightman, MD, assistant clinical professor of Obstetrics, Gynecology, and Reproductive Science at Mount Sinai, told Health. "Typically, they can come, they go, they can cause some discomfort at times, rarely does someone need surgery for something like that."

After releasing the egg in ovulation, the follicle walls collapse and develop into the corpus luteum. The corpus luteum produces estrogen and progesterone to prepare for pregnancy. When fluid accumulates, the corpus luteum becomes a corpus luteum cyst.

"Sometimes the post-ovulatory cyst, which we call the corpus luteum cyst, can also become quite large and can rupture or burst, which can cause pain," said Dr. Brightman. Usually, the pain resolves itself on its own, the cyst goes away after two or three menstrual cycles. "But there are times when people need surgical intervention, although that's rather rare."

Endometriosis

Not all people with endometriosis experience cyst growth. "Endometriosis is the presence of little implants, or lesions that are similar to the uterine lining, outside the uterus. That doesn't necessarily mean there's going to be a cyst," said Dr. Brightman. Those implants are called uterine endometrial cells, and sometimes, when they grow outside the uterus, they attach to ovaries and can form endometriomas.

Endometriomas are also referred to as "chocolate cysts," Mary Rosser, MD, PhD, Assistant Professor of Obstetrics & Gynecology at Columbia University, told Health. That's because an endometrioma contains old blood and tissue.

"So it's old blood, tissue like you get from your uterine lining, and because the old blood is usually dark, that's how it's got its name of 'chocolate cyst," said Dr. Rosser. Usually, these are painful, but some people don't have symptoms and discover them on ultrasounds.

Pregnancy

It's normal for a corpus luteum cyst to form after fertilization, said Dr. Brightman, and it becomes important during pregnancy. That cyst will produce the hormone progesterone and support the embryo through the first trimester, after which the placenta can start making progesterone itself. For people who get pregnant through in vitro fertilization (IVF), "they take a supplemental progesterone because they don't have that cyst," Dr. Brightman said.

"There may be a cyst seen on the ovary when we're diagnosing a pregnancy on ultrasound," said Dr. Rosser. Again, these corpus luteum cysts produce estrogen and progesterone throughout the first several weeks of pregnancy until the placenta can effectively function on its own, after which point the cyst resolves itself. Most people don't experience pain or bleeding from the cyst, and many don't realize it's there at all. However, said Dr. Rosser, "if a patient has pain or bleeding, we ask them to come in for evaluation."

A Congenital Condition

Dermoid cysts are less common, according to the Office on Women's Health, and are a congenital condition, meaning they develop in the womb, so a person with one of these cysts has likely had it their entire life. "It develops from ovarian tissue and the eggs," said Dr. Rosser, because these embryonic cells become trapped during fetal development. "It can contain tissues that are not actually from the ovary, like fat cells, hair, teeth, skin, and bone. It's very interesting-looking if you remove it in the operating room."

Ovarian dermoid cysts are usually diagnosed once someone reaches a reproductive age (especially around age 30) because they can cause pain during the menstrual cycle. They're not often cancerous, but surgery may be indicated to remove them.

"Honestly, with ultrasound, if they're small, we frequently leave them alone," said Dr. Brightman. "If they get to be larger than about six centimeters or so, or if a woman is symptomatic, then (at our practice) we remove them, typically via laparoscopy."

Though balls of hair, teeth, and bone might sound scary, dermoid cysts are fairly common and represent one in five abnormal growths on the ovaries beyond functional cysts. Your healthcare provider will have their own medical opinion on the appropriate time and conditions to remove cysts.

Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome is exactly what it sounds like—many cysts on the ovary. "They're tiny little follicular cysts that never go past a very early stage, and they are usually situated on the periphery of the ovary, and they look like a 'strand of pearls' on ultrasounds," said Dr. Rosser.

PCOS affects between 5% and 10% of cisgender women between the ages of 15 and 44. Many people discover it when they have trouble getting pregnant due to irregular menstrual cycles, per the Office on Women's Health.

People with PCOS are more likely to develop diabetes, high blood pressure, sleep apnea, and experience depression/anxiety, but researchers don't know whether PCOS causes these issues or vice versa or whether there's another underlying condition at play causing all of the above.

STDs and Pelvic Infections

A 2022 report from the Centers for Disease Control and Prevention (CDC) noted that gonorrhea, chlamydia, and syphilis were on the rise. Those infections can cause pelvic abscesses, which are sacs filled with pus. According to Johns Hopkins Medicine, the bacteria from these sexually transmitted infections (STIs) travel from the cervix into the uterus and may cause cysts to form. These cysts are filled with bacteria that can lead to sepsis if they rupture.

"Due to this infection, a patient will not feel well and usually has pelvic pain and fever," said Dr. Rosser. "That is why it is important for us to regularly screen for STIs and encourage women to engage in safe sexual practices."