The sexually mature vagina is kept moist by a discharge that originates from the vaginal wall and the cervix; its quantity and thickness vary with the menstrual cycle. A large quantity of clear mucus is produced during ovulation and discharge also increases before menstruation. In the vagina there are bacteria which form lactic acid and ensure that the vaginal fluid is acidic, a means of protection against vaginal infections. The discharge increases when blood supply to the vagina increases during sexual excitement and pregnancy. The quantity and acidity of the discharge both decrease after the menopause. Any unusual conditions in the vagina can alter the nature of the discharge. Soap, vaginal douches and the like may irritate the vagina and kill off acid-forming bacteria, which increases the likelihood of infection. An ill-fitting pessary or forgotten tampon can also lead to an abnormal discharge. Young girls may insert foreign bodies into the vagina when playing. The most common reason for abnormal discharge is vaginal infection. Infections of the cervix (gonorrhoea and genital herpes) also cause abnormal discharge. Erosion of the cervix, or a polyp, results in reduced discharge without demonstrable infection. A complete examination should be carried out if the discharge is protracted, especially if blood is also being lost. A smear test is most useful. Treatment of the discharge depends on the cause. Medication can be administered for bacterial and fungus infections. Sexual partners should also take medication, because otherwise the infection may pass from one partner to the other and back again. It is also possible to attempt to counteract fungus infections by inserting a tampon saturated with natural yoghurt and removing it after a few hours. The yoghurt contains lactic acid bacteria which can restore normal acidity. Gynaecological abnormalities are treated by the gynaecologist.