Ovarian Cysts

Ovarian cysts are fluid-filled or semi-solid sacs that form on or within one or both ovaries. The ovaries are two small, almond-shaped organs located on either side of the uterus, responsible for producing and releasing eggs and for making the hormones oestrogen and progesterone. Ovarian cysts are extremely common — most women who have periods will develop at least one ovarian cyst at some point in their lives, often without ever knowing it.

The great majority of ovarian cysts are harmless, cause no symptoms, and resolve on their own within a few menstrual cycles without any treatment at all. However, some cysts can grow large, cause pain, or — in a smaller number of cases — indicate an underlying condition that needs further evaluation or treatment. Understanding the different types of ovarian cysts, their causes, and when a cyst needs closer attention can help you feel more confident and less anxious if one is found during a routine scan or examination.

Types of Ovarian Cysts

Ovarian cysts are broadly divided into two categories — functional cysts, which are related to the normal menstrual cycle, and pathological cysts, which arise from abnormal cell growth. Each category includes several specific types.

Follicular Cyst: The most common type of functional cyst, forming when the fluid-filled sac (follicle) that normally releases an egg during ovulation fails to rupture and release the egg, and instead continues to grow. Usually resolves on its own within one to three menstrual cycles.
Corpus Luteum Cyst: Another common functional cyst, forming when the follicle releases its egg as normal but then reseals and fills with fluid or blood instead of breaking down as it usually would. Often resolves on its own, though it can occasionally cause the ovary to twist or bleed.
Dermoid Cyst (Mature Teratoma): A pathological cyst that develops from cells present since birth, and may contain tissue such as hair, skin or teeth. Usually benign, but can grow large and increase the risk of ovarian torsion if not monitored or removed.
Cystadenoma: A pathological cyst that develops from cells on the outer surface of the ovary, filled with a watery or mucous-like fluid. Can grow quite large and, while typically benign, generally requires surgical removal.
Endometrioma: Forms when tissue similar to the lining of the uterus (as seen in endometriosis) attaches to and grows within the ovary, sometimes referred to as a “chocolate cyst” due to the dark, old blood it contains. Often associated with pain during periods and intercourse.
Polycystic Ovaries: Seen in polycystic ovary syndrome (PCOS), where the ovaries contain multiple small, immature follicles rather than one or more larger cysts. This is a distinct hormonal condition rather than a single cyst requiring individual treatment.

How Ovarian Cysts Form

Understanding the normal menstrual cycle helps explain why ovarian cysts are so common:

Normal follicle development: Each month, a fluid-filled follicle develops on the ovary to nurture a maturing egg, growing to about 2cm before releasing the egg at ovulation.
When a functional cyst forms: If the follicle does not release its egg as expected, or reseals after ovulation instead of breaking down, it can continue to fill with fluid, forming a functional cyst — the most common type of ovarian cyst.
Hormonal influence: Hormonal fluctuations, including those related to fertility treatment, can increase the likelihood of functional cysts forming.
Pathological growth: Pathological cysts, by contrast, arise from abnormal growth of cells within or on the ovary, unrelated to the normal monthly cycle, and do not resolve on their own the way functional cysts often do.
Associated conditions: Conditions such as endometriosis or pelvic inflammatory disease can lead to cyst formation through inflammation or the abnormal growth of tissue on or around the ovary.

Symptoms of Ovarian Cysts

Most ovarian cysts cause no symptoms at all and are often discovered incidentally during a routine pelvic examination or scan performed for another reason. Larger or more significant cysts may cause:

Pelvic pain or a dull ache in the lower back, often on one side
A feeling of fullness, heaviness or bloating in the abdomen, particularly on one side
Pain during sexual intercourse
Painful or irregular periods
Difficulty emptying the bladder or bowels fully, or needing to urinate more frequently, if the cyst presses on nearby structures
Breast tenderness, particularly with functional cysts related to hormonal fluctuation
A noticeable swelling or mass in the abdomen, in the case of very large cysts

Certain symptoms warrant urgent medical attention, as they may indicate a complication such as cyst rupture or ovarian torsion: sudden, severe pelvic or abdominal pain, pain accompanied by fever, or pain together with nausea and vomiting. These symptoms should never be ignored or “waited out,” and prompt assessment is important.

What Causes Ovarian Cysts

Several factors and conditions can lead to the formation of ovarian cysts:

Hormonal fluctuations: Normal hormonal changes during the menstrual cycle are responsible for the majority of ovarian cysts, and fertility medications that stimulate ovulation can also increase the likelihood of functional cysts forming.
Endometriosis: Endometrial tissue that attaches to the ovary can develop into an endometrioma, a cyst that can be particularly painful during periods and intercourse.
Pregnancy: A corpus luteum cyst often forms in early pregnancy to support the pregnancy hormonally, and is usually harmless, though it occasionally persists and requires monitoring or removal later in pregnancy.
Pelvic inflammatory disease: Severe pelvic infection can spread to the fallopian tubes and ovaries, sometimes resulting in cyst formation as part of the inflammatory process.
Polycystic ovary syndrome (PCOS): A hormonal condition in which the ovaries develop numerous small, immature follicles, associated with irregular periods and other hormonal symptoms.
Previous ovarian cysts: A history of ovarian cysts increases the likelihood of developing further cysts in the future.

Risk Factors for Ovarian Cysts

Anyone with ovaries can develop an ovarian cyst, but certain factors increase the likelihood:

Age: Ovarian cysts are more common in women who have not yet gone through menopause, as functional cysts are directly related to ongoing ovulation.
Pregnancy: Cysts, particularly corpus luteum cysts, are more likely to form during pregnancy.
History of ovarian cysts: Having had an ovarian cyst previously increases the likelihood of developing another one.
Endometriosis: Women with endometriosis have a higher risk of developing endometriomas.
Polycystic ovary syndrome: Women with PCOS or other hormonal disorders have an increased likelihood of developing ovarian cysts.
Fertility treatment: Medications used to stimulate ovulation as part of fertility treatment can increase the risk of functional cysts.
Smoking: Some studies suggest smoking may be associated with a higher risk of developing certain types of ovarian cysts.

Possible Complications of Ovarian Cysts

Most ovarian cysts do not cause serious complications, but certain situations require prompt recognition and treatment:

Ovarian torsion: A cyst that grows large enough can cause the ovary to twist on the ligaments that support it, cutting off its blood supply. This causes sudden, severe pain and is a surgical emergency requiring urgent treatment to try to preserve the ovary.
Cyst rupture: A cyst can rupture, or burst, causing sudden, sharp pain and sometimes internal bleeding; larger cysts are more likely to rupture, and while many cases settle with rest and pain relief, some require urgent assessment.
Bleeding: Some cysts, particularly corpus luteum cysts, can bleed into themselves or into the pelvic cavity, causing pain and, in some cases, requiring treatment.
Impact on fertility: Certain cysts, particularly endometriomas or those requiring surgical removal of ovarian tissue, may affect ovarian reserve and fertility, which is an important consideration in younger women who wish to conceive in the future.
Ovarian cancer: The great majority of ovarian cysts are benign, but cysts that develop after menopause, or that have certain features on imaging, carry a higher likelihood of being cancerous, which is why such cysts are evaluated and monitored more closely.

How Ovarian Cysts Are Diagnosed

Ovarian cysts are often found incidentally, and further tests are used to characterise the cyst and determine whether treatment or monitoring is needed.

Pelvic Examination: A physical examination to feel for any lumps, swelling or tenderness in the pelvic area, often the first step in identifying a possible ovarian cyst.
Pelvic Ultrasound: The primary imaging test for ovarian cysts, usually performed transvaginally for the clearest view, allowing assessment of the cyst's size, location and characteristics (such as whether it is simple fluid-filled or has solid components).
Blood Test (CA-125 and Others): A blood test that may be used, particularly in postmenopausal women or when a cyst has concerning features on ultrasound, to help assess the likelihood of a cyst being cancerous; it is not a stand-alone diagnostic test, as levels can be raised by many benign conditions too.
CT or MRI Scan: May be used for further characterisation of a complex or large cyst, or to assess the pelvis and surrounding structures in more detail before planning treatment.
Laparoscopy: A minimally invasive procedure in which a thin camera is inserted through a small incision in the abdomen to directly visualise the ovaries and pelvic organs; cysts identified this way can often be removed or biopsied during the same procedure.

Living with an Ovarian Cyst

If you have been diagnosed with an ovarian cyst that does not require immediate treatment, your doctor will usually recommend a period of monitoring, typically involving a repeat pelvic ultrasound after a few weeks to months to check whether the cyst has resolved, remained stable, or changed in size or appearance.

During this time, it is helpful to keep track of your symptoms — including pain, changes to your periods, or any new symptoms — and to seek prompt attention if you experience sudden or severe pain, as this could indicate a complication such as torsion or rupture. Most women with a simple, small functional cyst can continue their usual daily activities, including exercise, without restriction, although your doctor may advise some caution with very vigorous or high-impact activity if a larger cyst is present, given a small increased risk of torsion.

Attending your follow-up scans as recommended is the most important part of monitoring, as it allows any change in the cyst to be identified and managed promptly.

Can Ovarian Cysts be Prevented

Because most ovarian cysts are a normal, expected part of the menstrual cycle, they cannot always be prevented — but a few measures may help reduce your risk or allow earlier detection:

Attend regular gynaecological check-ups: Routine pelvic examinations and scans can help detect ovarian cysts early, before they grow large or cause complications.
Consider hormonal contraception if appropriate: For women who experience recurrent functional cysts, hormonal birth control may help reduce how often new cysts form by preventing ovulation.
Manage related conditions: Good management of endometriosis, PCOS or pelvic inflammatory disease may help reduce the likelihood of cyst-related complications.
Be aware of your body: Paying attention to changes in your periods, new pelvic pain, or bloating, and seeking medical advice when something feels different or persistent, supports earlier detection.
Avoid smoking: Reducing or avoiding smoking supports overall reproductive and gynecological health.