Bacterial vaginosis, also known as vaginal bacteriosis, is the most common cause of vaginal infection for women of childbearing age.

It frequently develops after sexual intercourse with a new partner, and it is rare for a woman to have it if she has never had sexual intercourse.

Bacterial vaginosis (BV) also increases the risk of developing a sexually transmitted infection (STI). However, BV is not considered an STI.

BV is the vaginal infection most likely to affect women between the ages of 15 and 44 years.

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An imbalance in vaginal bacteria can lead to bacterial vaginosis.

BV may be present without symptoms, but if symptoms occur, they include vaginal discharge, burning, and itching.

Vaginal discharge may:

  • be watery and thin
  • be gray or white in color
  • have a strong and unpleasant smell, often described as fishy

Less commonly, there may be:

  • a burning sensation during urination
  • itching around the outside of the vagina

Between 50 and 75 percent of women with BV have no symptoms. BV alone is not considered harmful, but complications can arise.


Complications that have been linked to BV include a higher risk of:

  • HIV infection, as BV increases susceptibility to the virus
  • STIs, such as the herpes simplex virus, chlamydia, gonorrhea, and human papilloma virus (HPV)
  • post-surgical infection, for example, after a termination or a hysterectomy

Possible complications of BV during pregnancy include:

  • early, or preterm, delivery
  • loss of pregnancy
  • the amniotic sac breaking open too early
  • postpartum endometritis, an irritation or inflammation of the lining of the uterus after delivery
  • tubal factor infertility, caused by damage to the fallopian tubes, which connect the ovaries to the uterus
  • chorioamnionitis, an inflammation of the membranes surrounding the fetus, known as the chorion and the amnion

Chorioamnionitis significantly increases the chance of an early delivery. If the newborn survives, they have a higher risk of cerebral palsy.

In-vitro fertilization (IVF) may be less likely to succeed if a woman has BV.

BV also increases the risk of pelvic inflammatory disease (PID), an infection and inflammation of the upper female genital tract that can have severe consequences, including infertility.

BV is caused by an imbalance of naturally occurring bacterial flora, the usual bacteria found in a woman’s vagina. Why this happens is not clear.

It is different from candidiasis, a yeast infection, or Trichomonas vaginalis (T. vaginalis), or trichomoniasis, also known as trich. These are not caused by bacteria

The role of bacteria

All parts of the body have bacteria, but some are beneficial while others are harmful. When there are too many harmful bacteria, problems can arise.

The vagina contains mostly “good” bacteria and some harmful bacteria. BV occurs when the harmful bacteria grow in numbers.

A vagina should contain bacteria called lactobacilli. These bacteria produce lactic acid, making the vagina slightly acidic. This prevents other bacteria from growing there.

Lower levels of lactobacilli may cause the vagina to become less acidic. If the vagina is not as acidic as it should be, this can give other bacteria the chance to grow and thrive. However, exactly how these harmful bacteria are linked with BV is not known.

Risk factors

Any woman can develop BV, but some behaviors or activities can increase the risk.

These include:

  • douching, or using water or a medicated solution to clean the vagina
  • having a bath with antiseptic liquids
  • having a new sex partner
  • having multiple sex partners
  • using perfumed bubble baths, vaginal deodorants, and some scented soaps
  • smoking
  • washing underwear with strong detergents

BV cannot be caught from toilet seats, bedding, swimming pools, or touching objects.

BV often clears up without treatment, but women with signs and symptoms should seek treatment to avoid complications.

Treatment may not be needed if there are no symptoms. Sometimes BV can appear and disappear for no apparent reason.

If there is an abnormal vaginal discharge, it is important to see a doctor as soon as possible. A doctor can diagnose BV and rule out other infections, such as gonorrhea or trich.

Untreated BV can also lead to complications, especially during pregnancy.

Some doctors recommend giving BV treatment to all women who will be undergoing a hysterectomy or termination, before the procedure, regardless of symptoms.

Male partners do not usually need treatment, but they can spread BV between female sex partners.

Antibiotic medication

Antibiotics are effective in up to 90 percent of cases, but BV often comes back again within a few weeks.

Metronidazole is the most common antibiotic for BV.

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Oral antibiotics are normally effective against BV.

It is available in the following forms:

  • Tablets: Taken orally, twice daily for 7 days. It is seen as the most effective treatment, and the preferred treatment if the woman is breastfeeding or pregnant.
  • A single tablet: Taken orally as a one-time dose. BV is more likely to return with this treatment, compared with the 7-day tablet course.
  • Gel: Applied to the vagina once daily, for 5 days.

Metronidazole reacts with alcohol. The combination can make the patient feel very ill. Individuals taking metronidazole should not consume alcohol for at least 48 hours afterward.

Clindamycin is an alternative antibiotic. It may be used if metronidazole is not effective, or if the infection recurs.

When taking clindamycin, barrier contraception methods, such as latex condoms, diaphragms, and caps may be less effective.

Tinidazole is another antibiotic that is sometimes used to treat BV if metronidazole does not work or if BV recurs. It is taken by mouth as a single dose. Alcohol must be avoided when taking this medication.

If the following happens, further tests will be needed:

  • symptoms persist
  • symptoms go away but come back
  • the patient is pregnant

If symptoms resolve after completing a course of antibiotics, the woman will not have to be tested for BV again.

Recurring symptoms

Around 30 percent of women whose symptoms disappear with treatment will have a recurrence within 3 months, and 50 percent will have a recurrence within 6 months.

This may be treated with a 7-day course of oral or vaginal metronidazole or clindamycin. If the previous treatment was by mouth, vaginal treatment might work better the second time, and if the first treatment was vaginal, the follow-up treatment should be by mouth.

If more than three episodes occur within 12 months, the doctor may prescribe a vaginal metronidazole gel to use twice a week for 3 to 6 months.

The doctor may be able to diagnose BV from a description of symptoms and a physical examination. They will look out for an unpleasant smell and a thin, white or gray discharge.

If the patient is sexually active and there is a chance that an STI is present, the doctor may order some diagnostic tests.

A swab or small plastic loop can be used to collect sample cells from the vaginal wall. The pH balance of the vagina may also be measured, to assess acidity levels.

No over-the-counter medication is approved for BV, but there is anecdotal evidence that probiotics can help treat BV.

A review of studies, published in January 2014, concludes:

Although the results of different studies are controversial, most studies have been in favor of the probiotics in the prevention or treatment of BV, and no adverse effects have been reported. Therefore, it may be helpful to recommend daily consumption of probiotic products to improve public health among women.”

However, more research is needed to confirm its effectiveness.

Some other home remedies have been suggested, but, since BV can lead to serious complications, anyone with symptoms should see a doctor.

There is no certain way to prevent BV, as the exact causes remain unclear. However, some tips can help prevent it.

These include:

  • practicing safe sex
  • not douching

The Centers for Disease Control and Prevention (CDC) note that BV rarely affects women who have never had sex.