Pus refers to purulent leukorrhea, which is usually thin, transparent and odorless. If there is yellow or yellow-green thick leukorrhea with a foul odor, it is considered purulent leukorrhea, which is mostly caused by bacterial infection. Most purulent leukorrhea is caused by bacterial infections. The common diseases that cause purulent leukorrhea are acute cervicitis or cervicitis, and endometritis, which can cause purulent vaginal discharge. There are also cancers of the reproductive organs that may cause purulent leukorrhea when the cancerous lesions become infected, such as endometrial, cervical or vaginal cancer when the local surface cancerous lesions become infected. Some patients also have foreign body residue in the vagina, and when the foreign body residue stimulates the local tissues, purulent discharge will appear. The above are the common causes of purulent leucorrhea.