The bleeding on the panties at the age of 12 but no menstruation may be that the girl is in the pre-menstrual period, ovarian function is not fully developed, before the first menstruation may appear a small amount of bleeding, which is normal, during this period should pay attention to rest, avoid overwork. In addition, the following causes can also be seen: 1. Trauma: due to the usual playful accidental injury, or straddling injury can lead to blood on the panties. The most commonly injured part of a straddle injury is the pubic area. A straddle injury in women can lead to hematoma of the labia and possibly a hymen tear, which requires conservative treatment or surgical repair depending on the severity of the injury. If a foreign body is mistakenly put into the vagina, it can also lead to injury, infection and bleeding. Foreign bodies in the vagina can be removed through colposcopy, etc. 2. Reproductive system diseases: Reproductive system tumors and vaginitis can lead to blood flowing out of the vagina. Patients with tumors of the reproductive system should seek medical attention in time to avoid further progress. 3. Diseases of the urinary system: urethral prolapse refers to the prolapse of the urethral mucosa outside the urethral orifice, which may lead to bleeding from the urethra and contamination of the underwear. Tumors of the urinary tract can also lead to bleeding, and need to determine the treatment plan according to the pathological diagnosis to clarify the etiology, usually requiring surgical excision adjuvant chemotherapy and radiotherapy; 4. Other: anal bleeding occurs due to ruptured hemorrhoids, anal fissures, dry stool damage, anal polyps, etc., which can also stain the underwear, and should be promptly treated for the primary cause.