Bacterial Vaginosis: Causes, Symptoms & Effective Treatment

What Is Bacterial Vaginosis?

Bacterial vaginosis (BV) is a common vaginal condition caused by an imbalance of naturally occurring bacteria in the vagina. It occurs when protective lactobacilli decrease and harmful bacteria like Gardnerella vaginalis overgrow, leading to thin discharge with a characteristic fishy odor. BV affects approximately 29% of women globally.

The vagina naturally contains bacteria that form a balanced ecosystem. The most important of these are lactobacilli, which produce lactic acid that keeps the vagina slightly acidic (pH 3.8-4.5). This acidic environment prevents harmful bacteria from growing and causing problems. When this delicate balance is disrupted, bacterial vaginosis can develop.

In bacterial vaginosis, the number of protective lactobacilli decreases dramatically, while other bacteria—particularly Gardnerella vaginalis, Prevotella, Mobiluncus, and other anaerobic species—increase. This shift raises vaginal pH above 4.5, creating an environment where these bacteria thrive and multiply. The metabolic byproducts of these bacteria, especially amines, are responsible for the characteristic fishy odor associated with BV.

Unlike yeast infections, which are caused by fungal overgrowth and typically cause thick, cottage cheese-like discharge with intense itching, bacterial vaginosis produces thin, grayish-white discharge with a distinctive smell. Understanding this difference is important because the treatments are completely different—antifungals for yeast infections and antibiotics for BV.

Is Bacterial Vaginosis an STI?

Bacterial vaginosis is not classified as a sexually transmitted infection (STI), although there is a clear association with sexual activity. Women who have never had sexual contact rarely develop BV, and the risk increases with new sexual partners or multiple partners. However, BV can occur in women who are not sexually active, and unlike true STIs, male partners do not need treatment because they cannot develop or transmit the condition.

The exact mechanism by which sexual activity influences BV development is not fully understood, but researchers believe that semen, which is alkaline, may disrupt vaginal pH. Additionally, the introduction of new bacteria from a partner may disturb the existing vaginal microbiome. Using condoms and dental dams with new partners may help reduce the risk of developing BV.

How Common Is Bacterial Vaginosis?

Bacterial vaginosis is the most common vaginal condition in women of reproductive age (15-44 years). According to the World Health Organization, approximately 29% of women globally have BV at any given time, though prevalence varies significantly by population. In some studies, rates as high as 50-60% have been reported in certain communities.

Notably, many women with BV are unaware they have it. Studies suggest that 50-75% of women with BV are asymptomatic—they have the bacterial imbalance but experience no noticeable symptoms. This is significant because even asymptomatic BV can increase the risk of certain complications, including greater susceptibility to sexually transmitted infections.

What Are the Symptoms of Bacterial Vaginosis?

The most recognizable symptom of bacterial vaginosis is thin, grayish-white vaginal discharge with a distinctive fishy odor. The smell is typically stronger after menstruation and after unprotected vaginal intercourse. Some women also experience mild vaginal itching or burning during urination, though intense itching suggests a different condition.

When bacterial vaginosis does cause symptoms, they are usually mild to moderate in severity. The hallmark symptom is a change in vaginal discharge—specifically, an increase in thin, watery discharge that is grayish-white in color. Unlike the thick, clumpy discharge seen with yeast infections, BV discharge is homogeneous and coats the vaginal walls evenly.

The characteristic fishy odor is caused by amines produced by the overgrowth of anaerobic bacteria. This smell is particularly noticeable at two specific times: immediately after menstruation (when menstrual blood, which is alkaline, mixes with vaginal secretions) and after unprotected vaginal intercourse (when alkaline semen reacts with the amines). Many women first notice the problem in these situations.

Typical BV Symptoms

• Thin, grayish-white discharge: Usually not significantly increased in amount but changed in quality
• Fishy vaginal odor: Strongest after menstruation and unprotected sex
• Mild vaginal itching: Less intense than with yeast infections
• Burning during urination: Occasionally reported
• No symptoms: The majority of women with BV have no noticeable symptoms

When Symptoms Suggest Something Else

If you experience intense itching, thick white discharge, or significant redness and swelling, you may have a vaginal yeast infection rather than (or in addition to) BV. It's actually common to have both conditions simultaneously. If you notice any unusual discharge or odor changes, it's important to see a healthcare provider for proper diagnosis, as different vaginal conditions require different treatments.

Additionally, if discharge is yellow-green, frothy, or accompanied by pelvic pain, fever, or pain during sex, this may indicate a different infection such as trichomoniasis or pelvic inflammatory disease, which requires prompt medical attention.

What Causes Bacterial Vaginosis?

Bacterial vaginosis is caused by an imbalance in vaginal bacteria, where protective lactobacilli decrease and harmful bacteria increase. The exact trigger is unknown, but risk factors include new or multiple sexual partners, douching, lack of condom use, and having a female sexual partner. It is not caused by poor hygiene.

The vaginal microbiome is a complex ecosystem containing hundreds of bacterial species. In a healthy vagina, lactobacilli dominate this ecosystem, producing lactic acid and hydrogen peroxide that maintain an acidic environment (pH below 4.5) hostile to harmful bacteria. When something disrupts this balance, opportunistic bacteria can overgrow and cause BV.

Scientists have identified several bacteria associated with BV, most notably Gardnerella vaginalis. However, BV is not simply an infection with a single pathogen—it represents a complex shift in the entire vaginal bacterial community. Other bacteria commonly found in elevated numbers include Prevotella, Mobiluncus, Atopobium vaginae, and various anaerobic species that produce the characteristic amines responsible for the fishy odor.

Risk Factors for Developing BV

While the exact trigger for BV remains unclear, several factors have been consistently associated with increased risk:

• New sexual partner: Having a new sexual partner is one of the strongest risk factors
• Multiple sexual partners: The more partners, the higher the risk
• Douching: Vaginal douching disrupts the natural bacterial balance and is strongly discouraged
• Not using condoms: Unprotected sex exposes the vagina to alkaline semen that can alter pH
• Female sexual partners: Women who have sex with women have higher BV rates, possibly due to transmission of bacteria between partners
• IUD use: Some studies suggest intrauterine devices may slightly increase risk
• Smoking: Tobacco use has been associated with higher BV rates
• Lack of lactobacilli: Some women naturally have fewer protective bacteria

Importantly, BV is not caused by poor hygiene. In fact, excessive washing or use of harsh soaps, douches, or vaginal deodorants can disrupt the vaginal flora and increase BV risk. The vagina is self-cleaning, and cleaning the external genital area with plain water is sufficient.

How Is Bacterial Vaginosis Diagnosed?

Bacterial vaginosis is diagnosed through a pelvic examination and laboratory tests. Healthcare providers evaluate vaginal pH (elevated above 4.5 in BV), perform a whiff test for fishy odor, and examine discharge under a microscope for characteristic clue cells. At least three of four Amsel criteria must be present for diagnosis.

If you experience symptoms suggesting BV, your healthcare provider will perform a gynecological examination. During this exam, they will visually assess the vaginal discharge and may perform several simple tests to confirm the diagnosis. Unlike some conditions that require extensive testing, BV can usually be diagnosed quickly during a single office visit.

The Amsel Criteria

The most common diagnostic approach uses the Amsel criteria, a set of four clinical signs. At least three of the four must be present to diagnose BV:

1. Thin, homogeneous discharge: Gray-white discharge that coats the vaginal walls
2. Vaginal pH above 4.5: Measured using pH paper; normal vaginal pH is 3.8-4.5
3. Positive whiff test: Fishy odor when 10% potassium hydroxide (KOH) is added to a sample of discharge
4. Clue cells on microscopy: Vaginal cells covered with bacteria, giving them a stippled appearance

The presence of clue cells is considered the most reliable single indicator of BV. These are vaginal epithelial cells that have become coated with bacteria, making their normally smooth edges appear fuzzy or stippled when viewed under a microscope.

Other Diagnostic Methods

In some settings, healthcare providers may use alternative diagnostic tests:

• Nugent score: A more detailed laboratory method using Gram stain to evaluate vaginal bacteria; considered the gold standard for research
• Molecular tests: DNA-based tests that detect specific BV-associated bacteria
• Point-of-care tests: Rapid tests available in some clinics for quick diagnosis

Regardless of the method used, accurate diagnosis is important because BV, yeast infections, and other vaginal conditions require different treatments. Self-diagnosis is often inaccurate, so if you have persistent or recurrent symptoms, professional evaluation is recommended.

How Is Bacterial Vaginosis Treated?

Bacterial vaginosis is treated with prescription antibiotics, most commonly metronidazole or clindamycin. These can be taken as oral tablets or applied as vaginal gels or creams. Treatment typically lasts 5-7 days with cure rates of 80-90%. Your partner does not need treatment, but you should avoid alcohol if taking metronidazole.

The good news about bacterial vaginosis is that it responds well to antibiotic treatment. The CDC recommends several treatment options, all of which have similar effectiveness. The choice between oral and vaginal treatment often depends on patient preference, potential side effects, and other individual factors.

Recommended Treatment Options

According to CDC guidelines (2021), the following treatments are recommended:

• Metronidazole 500mg: One tablet taken orally twice daily for 7 days
• Metronidazole gel 0.75%: One full applicator (5g) inserted vaginally once daily for 5 days
• Clindamycin cream 2%: One full applicator (5g) inserted vaginally at bedtime for 7 days

Alternative Treatments

• Tinidazole 2g: Once daily orally for 2 days, or 1g once daily for 5 days
• Clindamycin 300mg: Twice daily orally for 7 days
• Secnidazole 2g: Single oral dose (newer option with convenience of one-time treatment)

Oral metronidazole is often preferred because it is inexpensive and highly effective, but it can cause nausea and a metallic taste. The vaginal gel formulations have fewer systemic side effects but require consistent daily application. Your healthcare provider can help you choose the best option for your situation.

What About Over-the-Counter Products?

There are no over-the-counter medications specifically approved for treating bacterial vaginosis. Some women try products containing lactic acid or vaginal probiotics to help restore the vaginal bacterial balance. While these products are generally safe, scientific evidence for their effectiveness in treating active BV is limited. They may be more useful for prevention of recurrence rather than treatment of current infection.

If you have been previously diagnosed with BV and recognize the symptoms, some countries allow pharmacists to dispense certain BV treatments without a prescription for women over 18. However, if symptoms persist or you're uncertain about your diagnosis, professional evaluation is recommended.

Do Partners Need Treatment?

Current evidence shows that treating male sexual partners does not prevent BV recurrence, so partner treatment is not routinely recommended. Male partners cannot get BV, and studies have not shown benefit from treating them. However, if you have a female sexual partner, she should be evaluated if she has symptoms, as BV may be more readily shared between female partners.

What About Bacterial Vaginosis During Pregnancy?

Bacterial vaginosis during pregnancy requires medical attention because it is associated with a small but significant increased risk of preterm birth, low birth weight, and postpartum infections. Pregnant women with symptomatic BV should be treated with oral metronidazole or clindamycin. BV cannot be transmitted to the baby.

If you are pregnant and suspect you have bacterial vaginosis, it is important to inform your healthcare provider or midwife. While BV is common during pregnancy and most cases do not lead to complications, untreated symptomatic BV has been associated with adverse pregnancy outcomes in some studies.

Potential Risks of Untreated BV in Pregnancy

• Preterm birth: Delivery before 37 weeks of pregnancy
• Low birth weight: Baby weighing less than 2,500 grams (5.5 pounds)
• Premature rupture of membranes: Water breaking before labor begins
• Postpartum endometritis: Infection of the uterine lining after delivery

It's important to note that these are associations found in research studies—most women with BV during pregnancy have healthy pregnancies and babies. However, because treatment is safe and effective, symptomatic BV during pregnancy should be treated.

Safe Treatment During Pregnancy

Metronidazole and clindamycin are considered safe during all stages of pregnancy. Oral metronidazole is often preferred because it treats not only vaginal BV but also any bacterial ascent toward the upper reproductive tract. Your healthcare provider will discuss the best treatment option for your specific situation.

Reassuringly, BV cannot be passed to the baby either during pregnancy or during delivery. The condition affects only the vagina and does not infect the baby.

What Complications Can Bacterial Vaginosis Cause?

Untreated bacterial vaginosis can increase susceptibility to sexually transmitted infections including HIV, chlamydia, and gonorrhea. It may also lead to pelvic inflammatory disease if bacteria spread to the uterus and fallopian tubes. Women having gynecological procedures should inform their provider of BV to reduce infection risk.

While bacterial vaginosis itself is not dangerous, leaving it untreated can lead to several potential complications. The disrupted vaginal environment in BV makes the vagina more vulnerable to other infections and can affect reproductive health.

Increased STI Susceptibility

One of the most significant concerns with BV is its association with increased acquisition of sexually transmitted infections. Research has shown that women with BV are:

• More likely to acquire HIV: Studies suggest 1.5-2 times increased risk
• More susceptible to herpes simplex virus (HSV)
• At higher risk for chlamydia and gonorrhea
• More likely to transmit HIV to partners if already infected

This increased vulnerability is thought to occur because BV causes inflammation and disrupts the protective mucus barrier, making it easier for pathogens to enter the body. For sexually active women, maintaining a healthy vaginal microbiome is an important component of STI prevention.

Pelvic Inflammatory Disease (PID)

BV bacteria can sometimes ascend from the vagina into the upper reproductive tract, potentially causing pelvic inflammatory disease—an infection of the uterus, fallopian tubes, and ovaries. PID can lead to chronic pelvic pain, scarring of the fallopian tubes, and infertility. While PID is more commonly caused by chlamydia and gonorrhea, BV-associated bacteria have been implicated in some cases.

Surgical and Procedural Complications

Having BV at the time of certain gynecological procedures increases the risk of post-procedure infections. This includes:

• IUD insertion: Both copper and hormonal IUDs
• Hysterectomy: Surgical removal of the uterus
• Dilation and curettage (D&C): Uterine scraping procedure
• Abortion procedures: Surgical pregnancy termination

If you are scheduled for any of these procedures and think you may have BV, tell your healthcare provider. They may want to test for and treat BV before the procedure to reduce infection risk.

How Can I Prevent Bacterial Vaginosis?

Preventing bacterial vaginosis involves maintaining healthy vaginal flora. Never douche, use condoms with new partners, limit the number of sexual partners, and avoid scented products near the vagina. Complete all prescribed treatment for BV to reduce recurrence risk. Probiotics may help some women prevent recurrence.

Because the exact cause of bacterial vaginosis is not fully understood, there is no guaranteed way to prevent it. However, several practices can help maintain a healthy vaginal bacterial balance and reduce your risk:

Proven Prevention Strategies

• Never douche: Douching is the single most harmful practice for vaginal health—it disrupts normal bacteria and significantly increases BV risk
• Use condoms or dental dams: Barrier protection with new or casual partners helps maintain vaginal pH
• Limit sexual partners: Having fewer partners reduces exposure to new bacteria that may disrupt your vaginal flora
• Avoid scented products: Don't use scented tampons, pads, soaps, or sprays near the vagina
• Wear breathable underwear: Cotton underwear allows air circulation and reduces moisture
• Complete antibiotic courses: If prescribed antibiotics for BV, take the entire course even if symptoms improve

What About Probiotics?

There is growing interest in using probiotics—particularly strains of Lactobacillus—to prevent BV recurrence. Some studies suggest that vaginal or oral probiotics may help restore and maintain healthy vaginal bacteria. However, scientific evidence is still mixed, and not all probiotic products are equally effective.

If you experience frequent BV recurrence, discuss probiotics with your healthcare provider. Products specifically designed for vaginal health, containing strains like Lactobacillus rhamnosus or Lactobacillus reuteri, may be more helpful than general probiotics. However, they should be considered a supplement to, not a replacement for, prescribed treatment.

Why Does Bacterial Vaginosis Keep Coming Back?

Bacterial vaginosis recurs in up to 50% of women within 12 months of treatment. Recurrence may occur because antibiotics don't fully eliminate biofilm-forming bacteria, the vaginal microbiome fails to restore normal lactobacilli, or ongoing exposure to risk factors continues. Suppressive therapy or extended treatment may help women with frequent recurrence.

One of the most frustrating aspects of bacterial vaginosis is its tendency to return after successful treatment. Initial antibiotic therapy has cure rates of 80-90%, but many women experience recurrence within weeks to months. Understanding why this happens can help guide prevention strategies.

Why BV Recurs

Several factors contribute to BV recurrence:

• Biofilm formation: BV bacteria form protective biofilms on vaginal cells that antibiotics cannot fully penetrate
• Incomplete lactobacilli restoration: After antibiotics clear BV bacteria, protective lactobacilli may not return in sufficient numbers
• Continued risk factor exposure: New partners, douching, or other risk factors can disrupt the vagina again
• Reinfection from female partners: BV bacteria may be shared between female sexual partners
• Individual vaginal microbiome characteristics: Some women simply have vaginal environments more prone to BV

Treatment for Recurrent BV

If you experience three or more episodes of BV per year, your healthcare provider may recommend:

• Suppressive therapy: Using metronidazole gel twice weekly for several months after initial treatment
• Extended initial treatment: Longer courses of antibiotics
• Boric acid suppositories: Intravaginal boric acid may help restore vaginal acidity (not during pregnancy)
• Probiotic supplementation: Vaginal or oral lactobacillus products

Managing recurrent BV often requires patience and trying different approaches. Work with your healthcare provider to find the strategy that works best for you.

When Should You See a Doctor?

See a healthcare provider if you have new or changed vaginal discharge, especially with a fishy odor, if symptoms don't improve after treatment, if BV recurs frequently, if you're pregnant, or if you have pelvic pain or fever. Self-diagnosis is often inaccurate, and proper diagnosis ensures correct treatment.

While bacterial vaginosis is common and treatable, it's important to seek medical care in certain situations:

• First episode of abnormal discharge: Other conditions can mimic BV, so initial diagnosis should be confirmed by a healthcare provider
• Symptoms persist after treatment: If symptoms don't improve within a week of completing antibiotics
• Frequent recurrence: If BV returns more than 2-3 times per year
• Pregnancy: Any vaginal symptoms during pregnancy should be evaluated
• New partner or multiple partners: To rule out STIs that may have similar symptoms
• Pelvic pain or fever: May indicate spread of infection to upper reproductive tract
• Planning gynecological procedures: BV should be treated before procedures like IUD insertion