An ovarian cyst is a sac filled with fluid or semisolid material that forms on or within one or both of your ovaries. Your ovaries are small organs in your pelvis that hold egg cells and make hormones, such as estrogen and progesterone.

There are different types of ovarian cysts, most of which are painless and harmless (benign). Usually, ovarian cysts don't cause symptoms. You likely won't know you have one unless your provider finds one during a routine pelvic exam or imaging procedure.

Rarely, ovarian cysts can cause complications. Scheduling regular pelvic exams and speaking with your provider about any symptoms you may be experiencing can help prevent any problems with a cyst.

What are the types of ovarian cysts?

Most ovarian cysts are functional cysts. They form in response to your body's changes during your menstrual cycle. Less commonly, ovarian cysts form for reasons unrelated to menstruation. 

Functional cysts 

Functional cysts are the most common type of ovarian cyst and aren't disease-related. They occur as a result of ovulation (the release of an egg from the ovary). These cysts can be a sign that your ovaries are functioning as they should. Functional cysts generally shrink over time, usually within 60 days, without specific treatment.

• Follicular cysts. A small sac in your ovary, called a follicle, releases an egg each month as part of your menstrual cycle. A follicular cyst forms when the follicle doesn't release an egg. Instead, the follicle fills with fluid and grows bigger.

• Corpus luteum cysts. After the follicle releases an egg, it forms a hormone-producing group of cells called the corpus luteum. A cyst forms when fluid collects in the corpus luteum, causing it to grow.

Sometimes, functional cysts are called simple cysts.