Decrease in the number of days of menstruation may be a physiological phenomenon, or it may be a symptom of certain diseases, such as uterine fibroids, uterine polyps, etc., and you should go to the hospital in time to find out the cause. 1. Physiological factors: Due to the change of environmental factors, irregular diet, frequent staying up late, lack of sleep, mental stress, depression and other external factors, may have a certain impact on menstruation, causing a decrease in the number of days of menstruation. 2. Pathologic factors: (1) Uterine fibroid: it is a benign tumor formed by proliferation of uterine smooth muscle tissue. Usually there will be abnormal menstruation (increased menstrual flow, longer or shorter duration of each menstruation, shorter cycles between menstrual intervals, etc.), abdominal lumps, increased leucorrhea, lower abdominal distension and other symptoms. (2) Uterine polyps: polyp-like tissue that grows from the mucous membrane and submucous layer of the uterus, like nasal polyps and intestinal polyps. Abnormal menstruation may occur, manifested by heavy menstrual flow, prolonged or shortened menstrual period, and shortened menstrual cycle; abnormal uterine bleeding may also occur, such as extra bleeding between menstrual periods, and postmenopausal vaginal bleeding. This symptom alone is not enough to diagnose the disease; it may also be caused by other factors, such as long-term use of short-acting contraceptives. It is recommended that if physiological causes are ruled out, you should go to the hospital in time, ask the doctor to clarify the cause of the disease, and follow the doctor’s instructions for targeted treatment.