There are several reasons for brown blood on underwear: first, the most common reason may be due to gynecological inflammation, such as common endometritis, vaginitis, tubal inflammation, pelvic inflammatory disease, etc., the most important of which is vaginitis. When there is inflammation in the vagina the permeability of the small arteries of the vaginal lining increases and inflammatory secretions leak out through the vessels onto the mucous membrane of the vaginal wall and these abnormal secretions flow out through the vagina and adhere to the underwear. Vaginitis is more often caused by bacterial infections, and the color of the discharge varies from one bacterial infection to another, so the most likely cause of brown blood on the underwear is vaginitis. Second, for older women should consider common gynecological tumors, such as uterine fibroids, uterine plasma adenomas, endometriomas, vaginal tumors and other neoplastic diseases when the abnormal growth of material is easily necrotic or even ulcerated, erosion may be discharged through the vagina, the color can also be brown and can adhere to the panties.