How often do you change sanitary napkins?

Science Popularization: the normal menstrual volume is 20-60ml, more than 80ml is excessive menstruation, less than 5ml is too little menstruation. Women with more menstruation are advised to change sanitary napkins every 1-2 hours. The quantity is not much also want to maintain every 4 hours to change, because menstrual blood is the hotbed of bacteria, not timely replacement is easy to get gynecological diseases. Focus