Vaginal Flora

Lactobacillus casei bacteria, SEM

What are the Vaginal Flora?

The vaginal flora are the bacteria that live inside the vagina. The normal vaginal flora are dominated by various lactobacillus species. Lactobacilli help to keep the vagina healthy by producing lactic acid, hydrogen peroxide, and other substances that inhibit the growth of yeast and other unwanted organisms. They maintain the vagina at a healthy pH of around 4.

This mildly acidic environment helps protect against infection. So do the other substances they produce. 

Why is a Healthy Vaginal Flora Important?

A hallmark of bacterial vaginosis (BV) is disruption of this normal vaginal flora and a loss of lactobacilli. This can not only be unpleasant in and of itself. It can also leave a woman more susceptible to HIV and other sexually transmitted infections. Bacterial vaginosis is actually caused by an overgrowth of bacteria that normally exist at low levels in the vagina. When the lactobacillus population is disrupted, these bacteria take over. 

The bacteria associated with BV make a number of volatile amines. They are what cause the distinctive odor associated with BV. This odor tends to be more present after sex, particularly unprotected sex. This is because the amines become smellier at the higher pH associated with semen. However, despite the association, BV is not caused by sperm.

In fact, the greatest evidence for sexual transmission of bacterial vaginosis is in lesbians. It is not clear whether BV can be transmitted during vaginal intercourse. 

How Can Healthy Vaginal Flora Be Restored?

One of the difficulties in treating BV and related conditions, such as yeast infections, is figuring out how to restore the normal vaginal flora.

Sometimes the bacterial populations return to normal proportions after treatment. Other times they don't. In order to help restore a lactobacillus dominated flora, a number of researchers are looking at probiotic pills and suppositories. These treatments would contain lactobacillus species. The hope is that those bacteria would grow and recolonize the vagina. To date, results have been somewhat positive, if preliminary. Still if they are borne out, probiotics may be a new way to improve vaginal health and restore a healthy vaginal flora.


Boskey ER, 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.

Boskey ER, Telsch KM, Whaley KJ, Moench TR, Cone RA. Acid production by vaginal flora in vitro is consistent with the rate and extent of vaginal acidification. Infect Immun. 1999 Oct;67(10):5170-5.

De Alberti D, Russo R, Terruzzi F, Nobile V, Ouwehand AC. Lactobacilli vaginal colonisation after oral consumption of Respecta(®) complex: a randomised controlled pilot study. Arch Gynecol Obstet. 2015 Oct;292(4):861-7. doi: 10.1007/s00404-015-3711-4.

Murina F, Graziottin A, Vicariotto F, De Seta F. Can Lactobacillus fermentum LF10 and Lactobacillus acidophilus LA02 in a slow-release vaginal product be useful for prevention of recurrent vulvovaginal candidiasis?: A clinical study. J Clin Gastroenterol. 2014 Nov-Dec;48 Suppl 1:S102-5. doi: 10.1097/MCG.0000000000000225.

Recine N, Palma E, Domenici L, Giorgini M, Imperiale L, Sassu C, Musella A, Marchetti C, Muzii L, Benedetti Panici P. Restoring vaginal microbiota: biological control of bacterial vaginosis. A prospective case-control study using Lactobacillus rhamnosus BMX 54 as adjuvant treatment against bacterial vaginosis. Arch Gynecol Obstet. 2015 Jul 5.

Taha TE, Hoover DR, Dallabetta GA, Kumwenda NI, Mtimavalye LA, Yang LP, Liomba GN, Broadhead RL, Chiphangwi JD, Miotti PG. Bacterial vaginosis and disturbances of vaginal flora: association with increased acquisition of HIV. AIDS. 1998 Sep 10;12(13):1699-706.

Vodstrcil LA, Walker SM, Hocking JS, Law M, Forcey DS, Fehler G, Bilardi JE, Chen MY, Fethers KA, Fairley CK, Bradshaw CS. Incident bacterial vaginosis (BV) in women who have sex with women is associated with behaviors that suggest sexual transmission of BV. Clin Infect Dis. 2015 Apr 1;60(7):1042-53. doi: 10.1093/cid/ciu1130.