If menstrual blood has a fishy smell, it is normal, but if there is any other smell, it is abnormal. If there is a fishy smell, then it is likely to be caused by infection, so it is recommended to do a gynecological examination after menstruation to find out whether there is pelvic inflammatory disease or endometrial inflammation. In addition, if the foul odor occurs during menstruation, the possibility of endometrial cancer should be ruled out. An ultrasound examination can be done after menstruation to find out whether there is echogenic unevenness in the endometrium and whether there are abnormal masses. In addition, if the menstrual blood has a fishy odor, it may also be caused by inflammation of the vagina, such as bacterial vaginosis caused by anaerobic infection, which often has a very fishy odor.