Sudden vaginal bleeding is not menstruation and is commonly caused by the following conditions: 1. It may be due to gynecological inflammation, which commonly includes pelvic inflammatory disease, endometritis, tubal inflammation and vaginitis. The most common are vaginitis and endometritis. When there is inflammation in these areas, the inflammatory secretions can lead to increased permeability of capillaries and small arteries, which can also cause mucosal edema, necrosis, and even ulcers. If the permeability of the blood vessels increases more seriously, it can lead to extravasation of blood, blood out of the blood vessels, and this outflow or exuded blood can flow out of the body via the vagina, thus causing the phenomenon of sudden bleeding below without menstruation. 2. For women with multiple sexual partners, it is important to suspect the possibility of sexually transmitted diseases, such as common condyloma acuminata, genital herpes, syphilis, gonorrhea, etc. This can lead to an increase in vascular permeability, which makes it easy for the blood vessels to rupture, and it can cause sudden vaginal bleeding.