The most common cause of foul smelling vaginal discharge is infection. For example, certain types of sexually transmitted diseases (STDs) may cause a discharge that smells bad, though some may not cause any symptoms at all. Interestingly, however, a woman may have an infection that is not sexually transmitted but still causes an unpleasant smell. This can occur, for example, when bacteria that are normally present in the vagina overgrow and cause infection. Sometimes the unpleasant smell is even caused by the presence of a foreign body, such as a tampon that has been left in the vagina for far too long.

Most women do have a slight natural odor in the vaginal area that may also extend to their discharge. In most cases, however, this discharge is not considered foul smelling; it is usually fairly mild in odor. If a woman does have a foul smelling discharge, however, it might be a sign of some type of infection. Some of the infections that are capable of causing foul smelling vaginal discharge are sexually transmitted, but many are not.

One of the most common causes of foul smelling vaginal discharge is an infection called trichomoniasis. Trichomoniasis is sexually transmitted and caused by a parasite. The discharge that develops when a woman is infected is often grayish, yellowish, or even greenish in color, and it usually has a watery in consistency. A woman may also have itching in the area when she has this infection as well as pain or bleeding during or after sexual intercourse. Pain during urination and swelling of the vaginal area may occur as well.

Bacterial vaginosis is another infection that can cause a whitish or grayish, foul smelling vaginal discharge. This infection develops when bacteria that are normally present in the vagina overgrow. It is not always spread through sexual activity, as some people who are not sexually active do develop it. In addition to the troublesome discharge typical of this infection, a woman may experience vaginal itching, pain or burning during urination or intercourse, and abnormal vaginal bleeding when she has this infection.

Foul smelling vaginal discharge also may develop because of the presence of a foreign body in the vagina. For example, if a woman forgets that she is wearing a tampon when her period ends, it could remain there unnoticed for a significant period of time. Eventually, it may cause an infection, with such symptoms as foul smelling vaginal discharge that is brownish or black.