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Bacterial Vaginosis


Updated May 23, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

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Bacterial vaginosis (BV) may not be a sexually transmitted disease, but it is often mistaken for one. Why? In order to understand bacterial vaginosis, it is important to understand the natural flora of the vagina.

The vagina is actually an ecosystem containing numerous species of bacteria. In a healthy women, those bacteria are primarily lactobacilli. Lactobacilli are called commensals, or useful bacteria, because they make lactic acid and peroxide. These byproducts of their normal metabolism help to keep the vagina at a slightly acidic pH of around 4, which protects against infection. Most STD bacteria are actually killed at pH 4, as are sperm.

When a woman has BV, the lactobacilli are replaced by a mix of other bacteria, including various types of gardnerella, mobiluncus, bacteroides, and mycoplasma. These bacteria do not produce lactic acid, and so the vaginal pH increases to above 4.5. They do, however, cause other problems, which brings us to the next question...

What does Bacterial Vaginosis Look Like?

It's not so much a question of what bacterial vaginosis looks like as what bacterial vaginosis smells like. Women with BV tend to have vaginal discharge with a fishy odor. This odor is more pronounced after unprotected sex, because the compounds that cause the odor smell more strongly at higher pH. When semen enters the vagina, it raises the pH to nearly 7 for a period of several hours. This is why many people think BV is caused by sperm.

Other symptoms of bacterial vaginosis include discharge, itching, and sometimes pain during urination.

What are the Risk Factors for Bacterial Vaginosis? What Causes It?

The cause of BV is poorly understoood. Although scientists do not yet understand why some women are susceptible to recurrent BV infections, there are several groups of women who have been shown to have increased risk of BV. These include:
  • Women who douche
  • Women with a new sex partner or multiple sex partners
  • Women who use IUDs as their primary form of contraception

For More Information


BV is a minor health condition that can have serious consequences. It increases a woman's susceptibility to HIV and other sexually transmitted diseases. It can also affect the outcome of a pregnancy. If you have symptoms of BV, talk to your doctor, particularly if you are intending a pregnancy or practice unprotected sex. Sources:

Boskey ER, and Cone RA, Whaley KJ, Moench TR. Origins of vaginal acidity: high D/L lactate ratio is consistent with bacteria being the primary source. Hum Reprod. 2001 Sep;16(9):1809-13.

The CDC Fact Sheet on Bacterial Vaginosis Accessed 5/9/07.

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