There are no known risk factors for the most common form of ovarian cysts – functional cysts. The cause of these cysts depends on the type of functional cysts:

• Follicular cysts. Some time during the menstrual cycle, the brain’s pituitary gland releases a large amount of luteinizing hormone (LH). This hormone tells the sac to release the egg. Normally, the egg bursts out of the sac and moves down the fallopian tube for fertilization. If the LH surge does not occur, the sac will not rupture. This traps the egg and starts the development of a cyst. Follicular cysts may be associated with a condition called polycystic ovarian syndrome (PCOS). However, not all women with PCOS develop these cysts.
  
  
• Corpus luteum cysts. When LH does surge and the egg is released, the ruptured sac (now called a corpus luteum) helps prepare the body for conception by producing large amounts of the hormones estrogen and progesterone. If conception does not occur, the cyst normally dissolves, which stops the production of hormones. The drop in hormone levels is the body’s signal to begin menstruation. Sometimes, the sac does not dissolve and the opening seals off. Fluid accumulates inside the sac, causing the corpus luteum to expand into a large, sometimes symptom-causing cyst.

There are also no known risk factors for abnormal cysts, with the exception of endometrioma cysts. Women with endometriosis are at higher risk of developing endometrioma cysts.