Ovarian cysts are fluid-filled sacs that form on or in an ovary. They are extremely common, most cause no symptoms at all, and the great majority are harmless and disappear on their own within a few weeks. Being told you have one on a scan is usually not a cause for alarm.

When to seek help urgently

Occasionally a cyst twists (torsion) or bursts. Both need prompt assessment. Go to hospital without delay if you develop:

  • Sudden, severe pain in the lower abdomen or pelvis
  • Severe pain with vomiting, fever, or feeling faint
  • A rapidly swelling, tender abdomen

The main types

  • Functional cysts — by far the most common. They form as a normal part of the menstrual cycle and usually resolve on their own.
  • Dermoid cysts — contain tissue such as hair or skin. Almost always benign, but they can grow and may need removing.
  • Cystadenomas — develop on the ovary surface and can become large. Usually benign.
  • Endometriomas — occur in women with endometriosis and can cause pain and fertility problems.

Symptoms

Most cysts are found by chance on a scan done for another reason. When there are symptoms, they may include:

  • Pain or a dragging ache in the lower abdomen or pelvis
  • Bloating or a feeling of fullness
  • Pain during sex
  • Irregular periods
  • Feeling full quickly when eating
  • Needing to pass urine more often

When a cyst needs following up

This is the question most women want answered, and the size on your scan report is the key.

The threshold we use is 4 cm (40 mm).

  • A simple cyst smaller than 4 cm does not need a routine follow-up scan. These are almost always functional and settle by themselves.
  • We do arrange follow-up if you are having symptoms, or if there are features that put you at higher risk of ovarian cancer — for example the appearance of the cyst on the scan, your age, or a relevant family history.
  • Larger cysts, and cysts with complex features on ultrasound, are followed up or investigated further.

If your scan report says a small simple cyst and you feel well, no news really is good news — there is no need to arrange repeat scans yourself.

Treatment

  • Watchful waiting — the right approach for most cysts. No treatment, just time.
  • Surgery — considered for cysts that are large, persistent, causing symptoms, or suspicious on imaging. This is usually done by keyhole surgery, removing the cyst and preserving the ovary where possible.

Most cysts are benign. Where imaging raises any concern, further tests are arranged before deciding on treatment.

Can they be prevented?

Not really, and there is no need to try. If you are using hormonal contraception anyway, it does reduce the formation of functional cysts — but it is not something to start purely for that reason. Attending for routine checks means anything that does need attention is picked up in good time.

The bottom line

Most ovarian cysts are harmless, cause no symptoms and go away on their own. Simple cysts under 4 cm need no routine follow-up unless you have symptoms or a higher risk of ovarian cancer. Seek urgent care for sudden severe pelvic pain, and see us if you have ongoing pain, bloating or a change in your periods.

References

  1. National Health Service. Ovarian cyst [Internet]. NHS; [cited 2026 Jul 22]. Available from: https://www.nhs.uk/conditions/ovarian-cyst/
  2. Royal College of Obstetricians and Gynaecologists. Patient information leaflets [Internet]. London: RCOG; [cited 2026 Jul 22]. Available from: https://www.rcog.org.uk/for-the-public/browse-our-patient-information/