Irregular vaginal bleeding is a complex condition. It varies from patient to patient depending on age, bleeding, site of bleeding, and the relationship between bleeding and cyclicity. In general, in adolescence, since the gonadal function is not yet mature, the cause of irregular bleeding is usually the inability of the ovaries to ovulate and the inability of the corpus luteum to form, resulting in persistent bleeding due to the instability of the endometrium. During the menopausal transition, ovarian function gradually declines and ovulation is also greatly affected, so the bleeding is also mostly caused by non-ovulation. However, the older you get, the more likely you are to have malignant tumors, so you should pay special attention to the possibility of malignant tumors when you have bleeding during or after menopause. Women of childbearing age should be especially aware of infections and abnormal pregnancies because of their frequent sexual activity. Other common problems such as uterine fibroids or ovarian tumors are found in all age groups. Bleeding can occur from any part of a woman’s reproductive tract, including the body of the uterus, cervix, vagina, and vulva. Although most bleeding comes from the body of the uterus, it is called “vaginal bleeding” regardless of where it originates, except for normal menstruation. Common causes of irregular vaginal bleeding are: 1. Ovarian endocrine dysfunction: can cause abnormal uterine bleeding, including anovulatory dysfunctional uterine bleeding and ovulatory menstrual disorders, as well as uterine bleeding due to follicular rupture during intermenstrual periods and a brief drop in estrogen levels. A small amount of vaginal bleeding in the days after birth is caused by a sudden drop in estrogen levels after leaving the mother’s body and shedding of the endometrium, which usually stops on its own and does not require treatment. Endocrine disorders and exogenous medications can cause irregular vaginal bleeding. 2.Uterine bleeding related to pregnancy: Irregular vaginal bleeding in women of childbearing age is most often a complication of pregnancy or abnormal pregnancy. Vaginal bleeding in early or mid pregnancy may be due to miscarriage; vaginal bleeding in late pregnancy is generally associated with preterm labor, placenta praevia, early placental abruption, rupture of the blood sinus at the edge of the placenta, contoured placenta, rupture of the vascular front of the sail placenta; rupture of the urethral meatus, vulvar and vaginal varices, cervical erosion, polyps, submucosal fibroids of the uterus, and cervical cancer can also cause vaginal bleeding during pregnancy. If vaginal bleeding occurs 40 to 50 days after menopause and there is vague pain in one side of the lower abdomen, there is a high possibility of unruptured ectopic pregnancy; if there is severe abdominal pain and signs of internal bleeding, it may be ectopic pregnancy ruptured. Irregular vaginal bleeding occurs around 8 to 12 weeks after menopause, with variable amount, dark red color, heavy early pregnancy reaction and rapid growth of uterus, which is disproportionate to the growth of pregnant uterus, then the possibility of staphyloma cannot be ruled out; if the vaginal bleeding continues after the operation to clear the uterus for staphyloma, it may be malignant staphyloma; if the above phenomenon occurs after delivery, miscarriage, ectopic pregnancy or staphyloma, the possibility of choriocarcinoma should be thought of. 3. Genital inflammation: Generally, inflammatory bleeding is not too much, and there is often an increase in abnormal leucorrhea. Inflammation of vulva, ulcers as well as urethral meatus can have small amount of bleeding. Trichomonas vaginitis and mycosis vaginalis are characterized by abnormal leucorrhea, while senile vaginitis is characterized by postmenopausal bleeding. Cervicitis, especially with cervical polyps, can have contact bleeding; cervical cancer, tuberculosis or syphilitic lesions caused by cervical ulcers can also have contact bleeding; endometritis occurring after abortion or full-term delivery has increased bloody leucorrhea; pelvic inflammatory disease can also be manifested as irregular bleeding or excessive menstrual flow situation. 4. Genital tumors: Both benign and malignant tumors of genital organs can cause irregular vaginal bleeding. Uterine fibroids are common benign tumors that cause vaginal bleeding. Submucosal fibroids often cause irregular uterine bleeding, while interstitial fibroids cause excessive menstruation. Ovarian tumors that secrete estrogen can also cause vaginal bleeding. Almost all other tumors are malignant, including vulvar, vaginal, cervical, endometrial, uterine sarcoma, and choriocarcinoma. Various malignant tumors of the vagina, cervix and uterine body can cause a small amount of bleeding, or contact bleeding i.e. bleeding after sexual intercourse, or bleeding after menopause. If vaginal bleeding is heavy, persistent or recurrent after many years of menopause, the possibility of endometrial cancer should be considered. Ovarian granulosa cell tumors often have irregular vaginal bleeding or excessive menstruation, and may also bleed after menopause. Intermittent vaginal discharge of bloody fluid should be alerted to the possibility of tubal cancer. 5.Injury, foreign body and exogenous hormone: Genital tract trauma such as vulvar and vaginal riding injury can cause bleeding; bleeding after newlywed sex, mostly due to hymen rupture, and individually due to vaginal dysplasia. Uterine bleeding can be complicated by IUD placement or IUD displacement; bleeding can also be caused by young girls playing with pins and other pins placed in the vagina. Improper use of estrogen or progestin (including improper use of health products containing sex hormones) and irregular use of oral contraceptives can cause irregular uterine bleeding. 6. Vaginal bleeding related to systemic diseases: Systemic diseases such as leukemia, aplastic anemia, thrombocytopenic purpura or other systemic diseases such as liver cirrhosis and nephritis can cause excessive menstrual flow or uterine bleeding. Irregular vaginal bleeding can be seen in women of different ages and has many causes. Therefore, no matter what happens in the case of irregular vaginal bleeding, it is important to go to the hospital for a detailed examination to identify the cause and then treat it according to the different causes, and do not take it lightly and delay the treatment.