There is no fixed time for changing sanitary napkins, but it is usually determined by the amount of menstrual flow. If you have a heavy period, you may need to change them every 3-4 hours or even 1-2 hours; in the late menstrual period, you can use pads if your period is low. In addition, if there is discomfort or conditions allow, you can change the sanitary napkin at any time or shorten the change time appropriately. It should be noted that the cervical opening is dilated during menstruation, and the menstrual blood easily breeds bacteria, which may go upstream and cause endometritis, etc. At the same time, the vulva is stimulated by moisture for a long time, which may lead to vulvar itching and skin redness. Therefore, you should try to avoid replacing sanitary napkins after menstruation has completely soaked through them, or not replacing them for a long time. In addition, women should avoid taking sitz baths and having sex during menstruation or when they have gynecological lesions, and pay attention to keeping warm and eating lightly. In daily life, it is also necessary to change underwear daily and wash the vulva daily to ensure local hygiene.