Why do cysts form on ovaries

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Last updated: April 8, 2026

Quick Answer: Ovarian cysts form primarily during the menstrual cycle when follicles fail to release an egg or don't dissolve after ovulation. Functional cysts, the most common type, affect many women of reproductive age, with studies showing up to 18% of postmenopausal women also develop them. Most cysts are benign and resolve spontaneously within 1-3 menstrual cycles, but persistent cysts larger than 5 cm may require medical evaluation. Polycystic ovary syndrome (PCOS) affects approximately 8-13% of women of reproductive age worldwide, often involving multiple small cysts.

Key Facts

Functional ovarian cysts are most common in women of reproductive age (15-49 years)
Approximately 8-13% of women worldwide have polycystic ovary syndrome (PCOS)
Most ovarian cysts (about 85%) are benign and resolve without treatment
Postmenopausal women have a 18% prevalence of ovarian cysts
Cysts larger than 5 cm often require medical monitoring or intervention

Overview

Ovarian cysts are fluid-filled sacs that develop on or within the ovaries, with the first documented descriptions appearing in ancient Greek medical texts by Hippocrates around 400 BCE. Modern understanding began with the development of ultrasound technology in the 1950s, which allowed for non-invasive detection. Today, ovarian cysts are classified into several types: functional cysts (follicular and corpus luteum cysts) which are most common, dermoid cysts (containing tissues like hair or teeth), cystadenomas (from ovarian surface cells), and endometriomas (associated with endometriosis). The prevalence varies significantly by age group, with functional cysts being most common in women of reproductive age (15-49 years), while postmenopausal women have different risk profiles. Diagnostic methods have evolved from manual pelvic exams to transvaginal ultrasound (developed in the 1980s), CT scans, and MRI, with CA-125 blood tests helping distinguish benign from malignant growths.

How It Works

Ovarian cysts form through several distinct mechanisms. During the normal menstrual cycle, follicles (small sacs containing immature eggs) develop on the ovaries each month. Typically, one follicle matures and releases an egg during ovulation, then transforms into the corpus luteum which produces progesterone. Functional cysts occur when this process is disrupted: follicular cysts form when a follicle doesn't rupture to release an egg and continues growing (reaching 2.5-10 cm), while corpus luteum cysts develop when the corpus luteum fills with fluid or blood instead of dissolving. Hormonal imbalances, particularly involving follicle-stimulating hormone (FSH) and luteinizing hormone (LH), often contribute to these disruptions. Other types form differently: dermoid cysts develop from embryonic cells that can produce various tissues; cystadenomas arise from ovarian surface epithelial cells; and endometriomas occur when endometrial tissue implants on the ovary. Polycystic ovary syndrome involves multiple small cysts due to hormonal imbalances that prevent regular ovulation.

Why It Matters

Ovarian cysts have significant clinical and quality-of-life implications. While most are harmless and resolve spontaneously, they can cause pelvic pain, bloating, and menstrual irregularities that affect daily activities. Approximately 5-10% of women require surgical intervention for cysts that persist, grow large (typically >5 cm), or cause complications like torsion (twisting) or rupture. Early detection is crucial because while most cysts are benign, ovarian cancer remains the fifth leading cause of cancer deaths in women, with cysts sometimes being early indicators. Proper management reduces unnecessary surgeries while ensuring timely treatment when needed. The economic impact includes healthcare costs for monitoring and treatment, while the psychological impact involves anxiety about cancer risk and fertility concerns, particularly for women with PCOS who may experience infertility.