Bacterial vaginosis (BV) is the most common vaginal infection in women of reproductive age. It happens when the balance of bacteria inside the vagina shifts: protective bacteria decline, and other types multiply in their place. BV often causes a noticeable fishy odor and unusual discharge, though many women have no symptoms at all.
What Happens Inside the Vagina During BV
A healthy vagina is dominated by bacteria called Lactobacillus, which produce antimicrobial compounds that keep other microbes in check and maintain a mildly acidic environment (a pH below 4.5). This acidity acts like a natural defense system.
When BV develops, Lactobacillus populations sharply decline and anaerobic bacteria (types that thrive without oxygen) take over. The most common organism found in BV is Gardnerella vaginalis, which forms a sticky biofilm along the vaginal walls. That biofilm shelters Gardnerella and other BV-related microbes, making the infection harder for your body to clear on its own. As these bacteria multiply, vaginal pH rises above 4.5, and the protective acidic environment breaks down.
What BV Looks and Feels Like
The hallmark symptom is a fishy odor, which often becomes stronger after sex. Discharge is typically thin and milklike in consistency, and it may appear gray, white, or greenish. Some women also notice mild itching or irritation, but BV rarely causes the intense itching or thick, clumpy discharge associated with yeast infections.
Roughly half of women with BV have no noticeable symptoms. In those cases, the infection is sometimes discovered during a routine exam or while testing for something else. Even without symptoms, BV can still affect your health, particularly during pregnancy or by increasing vulnerability to other infections.
What Raises Your Risk
BV isn’t a sexually transmitted infection in the traditional sense, but sexual activity is one of the strongest risk factors. Having a new sexual partner or multiple partners increases the likelihood of a bacterial shift. Women who have sex with women can also pass BV-associated bacteria between partners.
Douching is another major contributor. Washing inside the vagina with water, vinegar, or commercial products strips away Lactobacillus and disrupts vaginal pH. Scented soaps, sprays, pads, and tampons can do the same thing. The vagina is self-cleaning, so warm water on the external vulva is all that’s needed. Putting products inside the vaginal canal introduces chemicals and fragrances that alter the environment bacteria depend on.
Other factors linked to BV include smoking, using an IUD, and recent antibiotic use for unrelated conditions. Stress and hormonal changes can also play a role, though researchers are still working out the exact mechanisms.
How BV Is Diagnosed
Doctors typically diagnose BV using a set of clinical criteria. A diagnosis requires at least three of the following four findings:
- Thin, homogeneous discharge that coats the vaginal walls smoothly
- Clue cells visible under a microscope (vaginal cells covered in bacteria, giving them a stippled appearance)
- Vaginal pH above 4.5
- A fishy odor that becomes apparent when the discharge is exposed to a chemical solution during the exam
Some clinics use a lab-based scoring system instead, which grades a vaginal swab sample under a microscope. Either way, the visit is quick and results are usually available the same day.
Treatment and What to Expect
BV is treated with prescription antibiotics, either taken by mouth or applied as a vaginal gel or cream. Treatment courses are short, generally lasting five to seven days. Symptoms usually improve within two to three days of starting treatment, but finishing the full course is important to reduce the chance of the infection bouncing back.
The bigger challenge with BV is recurrence. Between 50% and 80% of women experience another episode within 6 to 12 months after finishing antibiotics. That’s a remarkably high rate, and it’s one reason BV can feel frustrating to deal with. The biofilm that forms during infection is difficult to fully eradicate, and if the underlying bacterial balance isn’t restored, the same cycle can restart.
For women with frequent recurrences, doctors sometimes recommend extended or suppressive antibiotic regimens. Probiotics containing Lactobacillus strains have also shown promise. A meta-analysis pooling data from 16 studies found that probiotic treatment produced significantly higher cure rates and lower recurrence rates compared to controls. However, results vary depending on the specific strains used and how they’re delivered, so probiotics work best as a complement to antibiotic treatment rather than a replacement.
Why BV Matters Beyond Discomfort
Left untreated, BV raises the risk of several more serious health problems. It increases susceptibility to sexually transmitted infections, including HIV, HPV, chlamydia, and gonorrhea. The mechanism is straightforward: BV causes inflammatory changes in the vaginal lining, making it easier for pathogens to enter the body. Women with BV who are exposed to HIV are at meaningfully higher risk of acquiring the virus, and BV can also increase the amount of HIV shed in the genital tract of women already living with the virus, raising transmission risk to partners.
BV is also linked to pelvic inflammatory disease, a condition where infection spreads to the uterus, fallopian tubes, or ovaries and can cause chronic pain or fertility problems.
BV During Pregnancy
Pregnant women with BV face additional risks. The infection has been associated with preterm delivery, early miscarriage, low birth weight, and postpartum uterine infections. These associations are well documented, though screening recommendations vary. Not all pregnant women are routinely tested for BV, so mentioning any unusual discharge or odor to your provider during prenatal visits matters.
Treatment during pregnancy uses the same antibiotics prescribed outside of pregnancy. The medications considered first-line for BV are safe during pregnancy, and treating an active infection is generally preferred over leaving it alone given the potential complications.
Practical Steps to Protect Vaginal Balance
You can’t guarantee you’ll never get BV, but several habits help maintain the bacterial environment that keeps it at bay. Avoid douching entirely. Wash the vulva with warm water only and skip scented soaps, body washes, and feminine hygiene sprays. Choose unscented pads and tampons. Wear breathable cotton underwear when possible.
Using condoms consistently reduces (though doesn’t eliminate) the bacterial exchange that can trigger BV. If you’re prone to recurrent episodes, talk with your doctor about whether a maintenance probiotic or extended treatment plan makes sense for your pattern. Keeping track of when episodes occur, whether they follow your period or coincide with other changes, can help identify personal triggers that are easier to manage once you recognize them.