These occur in two forms, namely "functional" and "organic". Symptoms may not be present but can include pressure or pain in the abdomen, problems with urine flow or pain during sexual intercourse. Rarely, a very large cyst can become twisted and stop its own blood supply, possibly causing nausea, fever or severe abdominal pain. Functional ovarian cysts form part of the normal functioning of the ovary and are always benign. They may be either "follicular cysts", produced by all menstruating women every month and reaching up to 2-3cm in diameter before they rupture at ovulation, or "corpus luteum cysts", which appear after ovulation and may grow to produce "hemorrhagic cysts" if ovulation does not occur or is delayed. Rupture of such a cyst can sometimes cause painful ovulation or bleeding, which is often moderate and resolves by itself. Organic ovarian cysts may be benign or malignant and are not linked to the functioning of the ovary. They occur as either "dermoid cysts", which are benign tumors that may nevertheless recur on either ovary and contain elements derived from the skin (hairs, sebum, teeth), or other organic cysts.