Irregular menstruation in young girls may be caused by immature ovarian development or by organic diseases. 1. Ovarian immaturity: when a girl has her first menstrual period, it means that she has just entered puberty, her ovaries are not yet mature, and the secretion of estrogen and progesterone is insufficient to stimulate the endometrium to form menstruation, so it causes irregular menstruation, which is a normal physiological phenomenon, and there is no need to worry too much. As the ovaries and uterus mature, the menstrual cycle will gradually become regular. 2. Organic diseases: Some girls with irregular menstruation may suffer from gynecological diseases or abnormal blood clotting mechanism, which may cause menstrual cycle disorders, unstable menstrual flow, or even amenorrhea. It is necessary to consult a doctor in time to find out the cause and actively treat the original disease. If a teenage girl has abnormal menstrual symptoms, she should go to a regular hospital in a timely manner to identify the cause of the abnormal menstrual cycle and treat it under the guidance of a doctor.