An ovarian follicle is a cellular structure found in the ovary where immature eggs mature, leading to ovulation and either pregnancy or menstruation. Human women are born with nearly a million ovarian follicles, each with the potential to grow into an egg with the potential for fertilization. These essential parts of female reproduction are normal beneficial and functional, however abnormal growth can lead to health problems such as ovarian cysts.

Through fetal development and childhood, about half of all ovarian follicles are reabsorbed by the body. This leaves a finite amount of immature eggs at puberty, which begin a cycle of growth and release typically on a monthly basis. In a normal menstrual cycle, over a dozen eggs begin the growth process, but one, called the dominant follicle, matures faster and is released through ovulation. After ovulation occurs, those ovarian follicles that have partially grown are usually reabsorbed by the body. In some cases, unreleased eggs can continue to grow, becoming a cystic structure.

There are three main segments of an ovarian follicle that each play a detailed role in the maturation of the egg. The oocyte is the actual egg, which uses the environment of the ovarian follicle to grow and eventually release for ovulation. Surrounding the egg is a coating of cells called granulosa, which respond to hormones in the body and promote the growth of the oocyte. The theca, which compose an inner and outer layer surrounding the granulosa, help provide the granulosa with a supply of estrogen-derived substances. Working together in the structure of the ovarian follicle, the theca and the granulosa provide the hormones necessary for the oocyte to mature.

If an ovarian follicle becomes too large, due to excess fluid trapped under the cellular wall, the overgrown structure is called an ovarian cyst. While typically benign and quite common in women after puberty, these cysts can cause considerable pain and discomfort if they burst, and may even require surgical removal in some cases. Follicular cysts are extremely common, and are most likely to burst during ovulation, causing a sharp pain or dull ache in the ovary.

Although almost all ovarian cysts are benign, some can be cancerous in nature. Cysts can be detected through ultrasound examinations, and many benign cysts dissipate or burst within a few months, causing some discomfort but no long term effects. Nevertheless, some doctors recommend visiting a health care professional or gynecologist if pain during ovulation occurs in order to rule out cancerous cysts. For benign follicular cysts, many doctors recommend taking over the counter pain relievers, applying heating pads or taking warm baths. Other treatment involves drug therapy to regulate hormones, decreasing the chances of follicle cysts.