The duration of each menstrual period is called the menstrual period, and the change of menstrual period from 5 days to 3 days may be a normal physiological phenomenon, or it may be caused by fatigue or mental stress, or it may be the existence of organic pathology. 1. Physiological factors: the normal menstrual period is generally 2 to 8 days, an average of 4 to 6 days. Occasionally, menstruation changes from 5 days to 3 days, and if there are no other uncomfortable symptoms and no obvious change in the amount of menstruation, it may be a normal phenomenon. In addition, if the age of more than 40 years old, this situation is normal is the physiological transition to menopause caused by the decrease in menstrual flow. 2. Endocrine factors: fatigue, stress, anxiety, environmental changes, weight loss, malnutrition and other causes of ovarian function abnormalities, thyroid function abnormalities may also lead to changes in the menstrual period, the need for a clear diagnosis under the guidance of a doctor and then treatment. 3. Organic lesions: If the menstrual period changes from 5 days to 3 days, and the amount of menstruation decreases significantly, it may be caused by pathologic factors, and there may be organic lesions, such as uterine adhesions, chronic endometritis, etc. If this situation persists, it is necessary to go to the hospital. If this situation persists, it is necessary to further clarify the cause of the disease in the hospital. Normally, you need to pay attention to relaxation, maintain a good state of mind can be, maintain a healthy lifestyle, comprehensive and rich in nutrition. If the amount of menstruation is not normal, it is recommended to go to the hospital specialist.