Bacterial Vaginosis - Not Quite an STD

Lactobacillus bacteria, SEM

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

The vagina is actually a complex ecosystem containing numerous species of bacteria. In a healthy woman, those bacteria are primarily lactobacilli. Lactobacilli are called commensals, or useful bacteria.

They make lactic acid and peroxide as part of their metabolism. These bacterial byproducts 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. (Interesting fact: lactobacilli are also one of the bacteria used to make live-culture yogurt. These are usually, but not always, different sub-species than are found in the vagina)

When a woman has BV, the lactobacilli are replaced by a mix of other bacteria. Usually, the BV bacteria include 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. This is 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.It isn't.

But semen makes the symptoms of BV worse. 

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 causes of BV are poorly understood. Scientists do not yet understand why some women are susceptible to recurrent BV infections. Still, 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
  • African American women

There is also growing evidence that BV may be transmitted between women who have sex with women. 


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.

For More Information



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Forcey DS, Vodstrcil LA, Hocking JS, Fairley CK, Law M, McNair RP, Bradshaw CS. Factors Associated with Bacterial Vaginosis among Women Who Have Sex with Women: A Systematic Review. PLoS One. 2015 Dec 16;10(12):e0141905. doi: 10.1371/journal.pone.0141905.

Thinkhamrop J, Hofmeyr GJ, Adetoro O, Lumbiganon P, Ota E. Antibiotic prophylaxis during the second and third trimester to reduce adverse pregnancy outcomes and morbidity. Cochrane Database Syst Rev. 2015 Jun 20;(6):CD002250. doi: 10.1002/14651858.CD002250.pub3. 

Wolrath H, Ståhlbom B, Hallén A, Forsum U. Trimethylamine and trimethylamine oxide levels in normal women and women with bacterial vaginosis reflect a local metabolism in vaginal secretion as compared to urine. APMIS. 2005 Jul-Aug;113(7-8):513-6. PubMed PMID: 16086821.