A normal, healthy vagina secretes odorless discharge or discharge with a slight odor. Smelly discharge is a sign that something is wrong. Most commonly, odors from vaginal discharge are caused by vaginitis or vaginosis, an inflammation of the cells lining the vagina (vaginal mucosa). Vaginitis -- inflammation of the vagina -- or vaginosis -- increased vaginal discharge without inflammation -- occurs when the normal balance of bacteria and yeast in the vagina is upset by an outside factor. Vaginitis and vaginosis can be extremely uncomfortable, but fortunately they are not serious and are easy to treat. Rarely, smelly discharge can be a sign of a more serious problem.
Normally, a type of bacteria called Lactobacillus flourish in the vagina. An invasion of anaerobic bacteria, which can be sexually transmitted, can kill off the Lactobacilli. The resulting infection can go unnoticed, or you might have mild symptoms of itching or burning. You might also secrete more vaginal discharge than usual, and it might have a fishy odor. The odor will be stronger after anything that increases the pH of the vagina, such as exposure to semen and menstrual blood, both of which are alkaline. The fishy odor is diagnostic for bacterial vaginosis. It's caused by the presence of chemicals called amines -- metabolic by-products of the bacteria -- in your discharge. One test for bacterial vaginosis is indelicately called the “whiff test,” and involves a vaginal swab, a drop of 10-percent potassium hydroxide to increase the pH and a sniff to detect any fishy odor.
Trichomoniasis infection is caused by the overgrowth of the protozoa T. vaginalis, often a low-level resident of a healthy vagina. Trichomoniasis is usually sexually transmitted, and also causes a smelly vaginal discharge. It is usually easy to distinguish from bacterial vaginosis because with trichomoniasis, the discharge is copious, frothy or bloody, and greenish yellow, in addition to being foul-smelling.
According to the book "Primary Care for Women," up to 75 percent of all women will experience a yeast infection at some point in their lifetime. Medically known as candidal vaginitis, a yeast infection is the result of the overgrowth of the normal vaginal-resident fungus Candida albicans. These infections may be caused by antibiotics, a weakened immune system, poor eating habits, stress, hormonal imbalances, diabetes and pregnancy. The primary complaint of women with a yeast infection is itching, but condition causes a smelly discharge as well. The discharge is thick and white, and its appearance is often compared to cottage cheese.
Rarely, vaginal smells can be a sign of a more serious condition, such as pelvic inflammatory disease (PID) or cervical cancer. It is always best to consult your gynecologist if you have smelly discharge.