Ovarian follicles store female egg cells and produce the reproductive hormones estrogen and progesterone, the Mayo Clinic states. Follicles grow every month, and during a woman's menstrual cycle a mature egg is released for potential fertilization.
Immature egg cells, or oocytes, grow inside follicles filled with fluid in preparation for ovulation, according to the University of Michigan Comprehensive Cancer Center. The eggs mature over a period of roughly two weeks until they are exposed to hormones that trigger the next stage of growth. The majority of eggs and follicles die off before full maturation, but the remaining dominant egg is released into the fallopian tube when the surrounding follicle bursts. Follicles damaged by drugs or medical treatments may prevent the ovaries from functioning correctly.