During the last stage of the menstrual cycle, normally a layer of endometriosis lining on the inside of the uterus is expelled, known as menstruation blood which instead some of the endometriosis tissues grows somewhere in the body causing endometriosis. They also react to hormone signals of the monthly menstrual cycle, builds up tissue, breaks it and eliminates it through menstrual period. Endometriosis is estimated to affect:

a) About 20 of women who have developed the new onset of severe menstrual cramps
c) About 25% of women with sub-fertility (less fertile than a normal couple)

Since they grow in somewhere other than in the uterus, when they break there is no way for the period blood to exit causing blood attaching to the organs or lining of the abdomen resulting in scars or adheresion as well as weakening the normal function of organs.

Most of the time, the endometriosis tissues do not travel far. It is commonly found within the pelvic region, on the lining of peritoneum, in the ovaries, and on the surface of the uterus's outside wall, but they can be anywhere in the body such as well as fallopian tubes, the cervix, the vagina, and even the vulva.

Endometriosis can vary in appearance. It may be clear or white, reddish, brown or blue black, and cysts. They can be classified according to stage of severity:

a) Minimal stage:
Top surface, few in number. Commonly they are found in the inside wall of uterus, ligaments and ovary.
b) Mild stage:
Deeper implants, greater numbers are presented. Commonly found in the same area as minimal stage.
c) Moderate stage:
Many implants, endometriotic cysts present, affecting ovary function, causing scar tissues and adheresion is also present.
d) Severe stage:
Intensive perionreal implants, large endometromas present and dense adheresion.

Each women experiences differently to endometriosis. Some women may have extensive endometrial tissues in their body but feel little or no pain at all, while other women may only be in the early stage of endometriosis but have excessive pain.