Cysts are fluid filled sacs that can occur anywhere in the body. Ovarian cysts form on or inside the ovaries, which are part of the reproductive system of a woman where eggs are formed. During a normal monthly cycle, an egg is released from the ovary into the fallopian tube, where it can be fertilized and carried to the uterus to grow as a baby. There are two basic types of ovarian cysts associated with the normal function of the ovaries:

• Follicle cysts: These cysts are formed when the body gets an egg ready but the follicle or sac holding the egg doesn’t break open to release the egg. In this case, the sac keeps growing, forming a follicle cyst. These cysts are typically harmless and rarely cause pain.

• Corpus luteum cysts: In a normal cycle, after the egg is released from the ovary, the sac where the egg was held dissolves and disappears. Corpus luteum cysts form when the sac does not dissolve. Instead, after the sac releases the egg, the sac seals itself closed, allow fluid to build up. These cysts can grow to be almost four inches in diameter. They can also bleed or twist the ovary and may be painful. If the cyst fills with blood, it can rupture which causes sharp pain and bleeding in the abdomen. Some fertility drugs main increase the risk of this type of cyst.

The good news about functional ovarian cysts is that they are rarely cancerous, and will usually go away on their own. Most women have one of these types of ovarian cysts at some time in their lives, and most go away without treatment in just a few months. However, if an ovarian cyst should rupture, it can cause serious medical problems. Regular gynecological checkups allow your doctor to watch for ovarian cysts and to monitor cysts for any changes that could cause problems.

Ovarian cysts cannot be prevented. But birth control pills can stop you from ovulating, which means you will be less likely to form new cysts.

Other types of ovarian cysts are less common but are more likely to require treatment.
Further reading: Some Ovarian Cysts Contain More Than Fluid

Sources:
National Women’s Health Information Center
Mayo Clinic