Bacterial Vaginosis (BV)

What happens in BV

A healthy vagina is dominated by lactobacilli, bacteria that produce lactic acid and keep the pH acidic (about 3.8 to 4.5). In BV, lactobacilli decline and a mix of other bacteria, including Gardnerella vaginalis, Prevotella, Atopobium (now Fannyhessea) and others, overgrow and form a sticky biofilm on the vaginal wall. The pH rises above 4.5, and these bacteria produce amines that cause the fishy smell.

BV is not caused by poor hygiene. In fact, washing inside the vagina makes it more likely.

Symptoms

• thin, watery, gray or off-white discharge that coats the vaginal walls
• a fishy odor, often stronger after sex (semen raises the pH) or during and after a period
• mild itching or irritation in some women, though this is less typical
• burning when urinating occasionally

About 50 to 75% of women with BV have no symptoms at all.

BV vs yeast infection vs trichomoniasis

Self-diagnosis is often wrong. Many women who treat themselves for yeast actually have BV, which antifungals will not cure.

Causes and risk factors

The exact trigger is not fully understood, but BV is strongly linked to sexual activity:

• a new sexual partner or multiple partners
• sex between women, where BV can pass between partners
• not using condoms
• douching or using vaginal washes, deodorants and scented products
• an IUD (copper IUD more than hormonal)
• smoking
• recent antibiotics

Hormonal contraception and consistent condom use are associated with lower risk. BV is not usually classed as a sexually transmitted infection, because it can occur in women who have never had sex, but sex plays a major role in spreading BV-associated bacteria. Male partners can carry these bacteria on the penis and in the urethra.

Diagnosis

A doctor or nurse will examine the vagina and take a swab. Diagnosis uses:

• Amsel criteria: at least 3 of 4: thin gray discharge, vaginal pH above 4.5, a fishy odor when potassium hydroxide is added (whiff test), and "clue cells" (vaginal cells coated with bacteria) on microscopy.
• Gram stain (Nugent score): a lab method.
• NAAT molecular tests: detect BV-associated bacteria, often in combination with yeast and trichomonas testing.

Testing for chlamydia, gonorrhea and trichomonas is often done at the same time.

Treatment

CDC-recommended treatments for symptomatic BV:

• Metronidazole tablets twice daily for 7 days, or
• Metronidazole gel inside the vagina once daily for 5 days, or
• Clindamycin cream inside the vagina at bedtime for 7 days

Alternatives include tinidazole, secnidazole (a single dose of granules) and clindamycin by mouth or as ovules.

Tips during treatment:

• Finish the full course even if symptoms clear.
• Avoid sex or use condoms until treatment is complete.
• Clindamycin cream can weaken latex condoms and diaphragms for several days.
• Avoid alcohol during and for about 72 hours after tinidazole or secnidazole; current CDC guidance no longer requires avoiding alcohol with metronidazole, but some people still prefer to.

Treating male partners

A 2025 randomized trial found that treating male partners at the same time, with oral metronidazole plus a topical antibiotic cream on the penis for 7 days, roughly halved BV recurrence in women in monogamous relationships. Ask your clinician whether partner treatment is appropriate.

Recurrent BV

About half of women have BV again within 12 months. Options include:

• a longer course of metronidazole, followed by twice-weekly metronidazole gel for 4 to 6 months
• boric acid vaginal suppositories after an antibiotic course (never by mouth, and not in pregnancy)
• partner treatment
• addressing triggers such as douching, smoking and copper IUD

Probiotic supplements and yogurt have not been proven to prevent BV, though research continues.

BV in pregnancy

BV in pregnancy is linked to preterm birth, low birth weight and infection after delivery. Pregnant women with symptoms should be tested and treated; oral or vaginal metronidazole and clindamycin are considered safe in pregnancy. Routine screening of pregnant women without symptoms is not recommended for most.

Complications

Untreated BV increases the risk of:

• catching HIV, chlamydia, gonorrhea, herpes and trichomonas
• pelvic inflammatory disease, especially after procedures
• infection after gynecological surgery
• preterm labor and other pregnancy complications

Prevention

• Do not douche; wash only the outer vulva with water or a mild, unscented cleanser.
• Avoid scented pads, wipes and bubble baths.
• Use condoms, and limit numbers of partners.
• Stop smoking.
• Wipe front to back and change out of wet or sweaty clothing.

Frequently asked questions

What are the main symptoms of bacterial vaginosis?

The main symptoms are thin, gray or white discharge and a fishy odor, often stronger after sex or during a period. Itching and burning are less common than with yeast infections. Many women with BV have no symptoms at all.

Is bacterial vaginosis an STI?

BV is not classed as a sexually transmitted infection, because it can occur without sex. However, sexual activity strongly influences it. New or multiple partners raise the risk, it can pass between female partners, and treating male partners reduces recurrence.

Can BV go away on its own?

Sometimes. Mild BV can resolve without treatment in some women. However, symptoms often persist or return, and BV raises the risk of other infections and pregnancy complications. Testing and treatment are recommended if you have symptoms or are pregnant.

Why does my BV keep coming back?

BV recurs in about half of women within a year because the biofilm can survive treatment, the vaginal bacteria take time to rebalance, and partners can reintroduce BV-associated bacteria. Longer suppressive treatment, partner treatment and avoiding douching can help.

How can I tell BV from a yeast infection?

BV causes thin gray discharge with a fishy smell and little itching. A yeast infection causes thick, white, clumpy discharge with intense itching and no strong odor. A quick pH test or swab from a clinician tells them apart reliably.