What Causes BV? The Bacterial Imbalance Behind Bacterial Vaginosis

What causes BV? Bacterial vaginosis happens when the normal balance of bacteria in the vagina changes. Protective Lactobacillus bacteria decrease, allowing other bacteria, particularly anaerobic bacteria, to grow in larger numbers.

The exact cause of BV is not always clear, but several BV causes and risk factors are well established. Douching, having a new or multiple sex partners, not using condoms, and smoking can increase the risk. BV is not caused by poor hygiene, and it is not usually an infection that a partner simply "gave" you.

In short, what causes bacterial vaginosis is a disruption in the vaginal microbiome. When protective bacteria decline and other bacteria overgrow, BV symptoms such as a fishy odor, thin gray or white discharge, and irritation can develop.

TL;DR: What causes BV?

• What causes BV? BV develops when protective Lactobacillus bacteria decrease and other vaginal bacteria overgrow, disrupting the normal vaginal microbiome.
• The exact cause of BV is not always known, but common BV risk factors include douching, having new or multiple sex partners, not using condoms, and smoking.
• BV is not caused by poor hygiene. Washing more, douching, or using internal cleansing products will not prevent BV and may increase the risk.
• BV is not classified as an STI, although sexual activity and changes in sexual partners can affect the vaginal microbiome and increase BV risk.
• Toilet seats, swimming pools, and normal use of tampons or pads are not established causes of BV.
• BV can come back after treatment. Biofilm formation and difficulty restoring a Lactobacillus-dominant vaginal microbiome may contribute to recurrent BV.

Not sure whether your symptoms sound like BV, a yeast infection, or something else? Try August AI's free Symptom Checker for a quick guide to what your symptoms may mean and how urgently you should seek care.

If your symptoms sound like BV, August's $39 online urgent care visit connects you with a US-licensed clinician who can review your symptoms and medical history and decide whether treatment is appropriate. Telehealth cannot perform a pelvic exam, test vaginal pH, or collect and examine a vaginal sample, so some symptoms may still require in-person testing.

What causes BV is a bacterial imbalance, not something you caught

What causes BV is a change in the vaginal bacterial microbiome, rather than one specific germ taking over from outside. Protective Lactobacillus species normally help keep the vagina acidic by producing lactic acid. When those bacteria become less dominant, other bacteria can multiply more easily.

The CDC lists several bacteria commonly associated with BV, including Gardnerella vaginalis, Prevotella species, Mobiluncus species, and Atopobium vaginae. CDC treatment guidelines describe BV as a polymicrobial condition, meaning several types of bacteria can be involved rather than one single cause.

Those bacteria can also form a biofilm, a structured layer attached to the vaginal lining. This is one reason BV can be difficult to fully clear and why it often comes back after treatment.

There is an important distinction here: researchers understand a lot about what happens during BV, but they still don't know exactly why it develops in every person. The CDC notes that the exact cause of BV is not fully understood.

What we do know is that a healthy vagina is usually dominated by Lactobacillus. When that balance changes, vaginal pH typically rises above 4.5 and bacteria associated with BV can become more dominant.

BV is also extremely common. It is the most common vaginal condition among women ages 15 to 44 in the United States.

BV is not a hygiene problem

Having BV is not evidence that you are unclean or that you failed to take care of yourself.

BV happens because the bacterial balance in the vagina changes. You cannot prevent that shift simply by washing more, and trying to clean inside the vagina can actually make the problem worse.

As UT Southwestern explains, BV is a common medical condition and is not a reflection of personal hygiene.

The vagina also does not need to be cleaned internally. The vulva the external genital area can be washed gently, but there is no need to put soap, washes, sprays, or other cleansing products inside the vagina.

What are the main BV risk factors?

There isn't one single reason someone develops BV. Several things can affect the balance of bacteria in the vagina, and sometimes there is no obvious trigger at all.

The CDC identifies several factors associated with a higher risk of BV, including:

• Having a new sex partner
• Having multiple sex partners
• Not using condoms
• Douching

Smoking has also been associated with BV in research studies.

Some of these factors are things you can change. Others aren't. Your vaginal microbiome is individual, and researchers still don't fully understand why Lactobacillus remains dominant in some people but becomes less dominant in others.

Douching and internal vaginal products

Douching is one of the clearest BV risk factors because it can disrupt the normal vaginal environment.

The same caution applies to products designed to change how the vagina smells or feels internally. If something is fragranced or marketed to "freshen" the inside of the vagina, it isn't treating the cause of BV.

In fact, trying to wash away a fishy odor can make the underlying bacterial imbalance harder to correct.

If you want to clean the area, stick to gentle external washing. There is no need to douche or use scented products inside the vagina.

Sex and changes in sexual partners

Sex is strongly associated with BV, but that does not make BV a conventional STI.

The CDC lists new or multiple sex partners and lack of condom use among factors associated with BV. Sexual activity can affect the vaginal microbiome, while semen can temporarily raise vaginal pH because it is more alkaline than the normal vaginal environment.

That helps explain why some people notice BV symptoms after sex without having "caught" one specific germ in the way they might catch chlamydia or gonorrhea.

The CDC notes that BV can occur in people who have never had sex, so sexual activity is not a requirement for developing it.

And having BV does not mean your partner cheated or gave you an STI.

If you've had a new sexual exposure, though, STI testing can still make sense. BV and an STI can occur at the same time.

Smoking

Smoking is associated with a higher risk of BV and may be linked to differences in the vaginal microbiome.

The exact biological pathway is still being studied, so it is more accurate to call smoking an associated risk factor rather than say that smoking directly causes every case of BV.

If you smoke, quitting has plenty of health benefits regardless. But you should not assume that smoking is the sole reason you developed BV.

Previous BV

If you've had BV before, you're more likely to experience it again.

That doesn't necessarily mean the first treatment was wrong. BV can return because getting rid of the bacteria is only part of the problem. The vaginal environment also needs to return to a more stable, Lactobacillus-dominant state.

Recurrence is common, so another episode isn't automatically evidence that you did something wrong or that your treatment failed.

Does an IUD cause BV?

Not necessarily.

Some studies have found an association between certain forms of contraception and BV, but an IUD isn't automatically the cause of recurrent BV. Having BV also does not mean you need to have a working IUD removed.

If you started having repeated BV episodes after getting an IUD, it's reasonable to mention the timing to your gynecologist or clinician. They can look at the whole pattern and discuss whether your contraception could be playing a role.

Don't remove or stop using contraception solely because of BV without discussing your options with a healthcare professional.

BV is not an STI, but sex can still affect your risk

This is one of the most confusing things about bacterial vaginosis because both of these statements are true:

BV is not classified as a sexually transmitted infection.

Sexual activity can increase the likelihood of developing BV.

BV isn't caused by one specific pathogen that simply moves from one person to another. Instead, it involves a change in the balance of bacteria already present in the vaginal environment.

But sex can influence that environment.

A new partner can introduce different bacteria. Semen can temporarily raise vaginal pH. And condomless sex is associated with a higher risk of BV.

The CDC also notes that BV is rarely seen in people who have never had sex.

None of this means that a BV diagnosis proves a partner cheated or gave you an infection.

It also doesn't mean you should skip STI testing after a new exposure. BV is associated with an increased risk of acquiring certain STIs, so the two issues can overlap.

Can BV spread between female sex partners?

BV-associated bacteria and similar vaginal microbiome patterns can occur between female sex partners, and BV is more common among women who have sex with women than in some other populations.

Partner management is more complicated than simply treating BV like chlamydia or gonorrhea, however.

If you have recurrent BV and a female sexual partner, talk with a clinician about the pattern, particularly if both partners have symptoms.

Can stress cause BV?

Stress is not considered a direct, established cause of BV.

Some studies have found an association between higher stress and a greater risk of BV. Researchers are looking at possible connections involving hormones, immune function, and the vaginal microbiome, but those mechanisms are not fully understood.

So the practical answer is simple:

Stress may affect your risk, but you don't get BV simply because you had a stressful week.

That's worth saying because BV already comes with enough reasons for people to blame themselves.

Stress reduction can still be good for your overall health, sleep, and wellbeing. But it shouldn't be presented as a treatment for an active BV infection.

Tight clothes, pools, toilet seats, and sugar are not established causes of BV

There are plenty of things people blame for vaginal infections that aren't established bacterial vaginosis causes.

These include:

• Toilet seats
• Swimming pools
• Hot tubs
• Normal use of tampons or pads
• Tight clothing
• Synthetic underwear
• Dietary sugar

Some of these are often discussed in connection with yeast infections, but BV and yeast infections are completely different conditions.

BV involves an imbalance in vaginal bacteria.

A yeast infection involves an overgrowth of Candida, a fungus.

That difference matters because the treatments are different, too. Over-the-counter antifungal creams can treat some yeast infections, but they do not treat BV.

As a general guide:

• BV: Thin gray or white discharge, often with a fishy odor
• Yeast infection: Thick white discharge with significant itching, usually without a strong fishy odor

Symptoms can overlap, and some people can have more than one condition at the same time. If you're not sure what you're dealing with, testing is more reliable than trying to diagnose yourself from discharge or odor alone.

If burning or irritation is your main symptom, this guide to what causes a burning sensation in the vaginal area covers some of the other possibilities.

Why do I keep getting BV?

If you're asking, "Why do I keep getting BV?", the answer usually isn't that you did something wrong.

Recurrent BV is common.

One possible reason is the polymicrobial biofilm associated with BV. Bacteria within a biofilm can be harder to eliminate than bacteria that are freely present in vaginal fluid. Researchers also think that difficulty restoring a stable Lactobacillus-dominant microbiome may contribute to recurrence.

Other factors can play a role, too. Sexual activity, changes in partners, condom use, douching, smoking, and individual differences in the vaginal microbiome may all affect the chance of BV returning.

The important point is that recurrence is a feature of BV, not a hygiene failure.

If BV keeps coming back, don't just keep trying different over-the-counter products. Talk with a clinician about whether you need:

• Repeat testing to confirm that it is actually BV
• STI testing when appropriate
• A different treatment regimen
• Longer-term suppressive treatment for multiple recurrences
• A discussion about whether partner treatment is appropriate in your situation

Partner treatment for recurrent BV is an evolving area. ACOG issued updated guidance in 2025 recommending that clinicians consider concurrent treatment of male sexual partners in some adults with recurrent symptomatic BV. This does not mean partner treatment is necessary for every episode. ACOG explains the updated recommendation here.

If repeat treatment is becoming a pattern, it may also help to compare Wisp and August for BV treatment, cost, and speed.

What can you do to reduce your risk of BV?

There is no guaranteed way to prevent every episode of BV. But you can avoid some of the factors known to increase your risk.

• Don't douche.
• Avoid fragranced products inside the vagina.
• Consider using condoms, particularly if you notice a pattern of symptoms after condomless sex.
• Avoid smoking or get support to quit if you smoke.
• Take prescribed BV treatment exactly as directed.
• If BV keeps returning, ask about a recurrence-management plan instead of repeatedly self-treating.

You can't control everything that affects your vaginal microbiome, and you don't need to.

The goal isn't to create a perfect routine. It's simply to avoid disrupting the vaginal environment unnecessarily and get appropriate care when symptoms show up.

When BV symptoms need a clinician instead of more home remedies

A typical BV episode isn't usually an emergency. But some symptoms shouldn't be assumed to be BV without medical evaluation.

Seek urgent medical care if you have:

• Severe pelvic or lower abdominal pain
• Fever or chills with pelvic pain or abnormal vaginal discharge
• Heavy or unusual vaginal bleeding
• Rapidly worsening symptoms

These symptoms can point to something other than uncomplicated BV, including pelvic inflammatory disease.

Book a visit soon if:

• You are pregnant and have new vaginal symptoms
• Symptoms don't improve after completing treatment
• Symptoms keep coming back
• You have a new sexual exposure and may need STI testing
• Your discharge or other symptoms are different from what you've experienced before

Talk to a Physician before starting treatment if:

• You are pregnant or may be pregnant
• You are considering boric acid
• You plan to use leftover antibiotics
• You've had a previous reaction to metronidazole or another medication
• You're not sure whether your symptoms are BV, yeast, or something else

For symptoms that don't require emergency care, August's $39 online urgent care visit connects you with a US-licensed clinician who can review your symptoms and history and decide whether treatment is appropriate.

Telehealth has limits. A video visit cannot perform a pelvic exam, test vaginal pH, or collect and examine a vaginal sample. If your symptoms are unclear, severe, recurrent, or suggest another infection, in-person testing may still be the better next step.

The Conclusion: BV is a microbiome imbalance, not a hygiene failure

What causes BV? A change in the balance of bacteria in the vagina.

Protective Lactobacillus bacteria become less dominant, other bacteria multiply, and the vaginal environment becomes less acidic. Researchers don't know exactly why this shift happens in every case, but factors such as douching, certain sexual exposures, lack of condom use, and smoking are associated with a higher risk.

Just as important is knowing what does not cause BV. Being "dirty," failing to wash enough, using a public toilet, or swimming in a pool are not established causes.

If you develop BV, don't respond by cleaning harder. Douching and internal cleansing products can disrupt the vaginal environment rather than fix it.

And if BV keeps coming back, don't blame yourself. Recurrent BV is common and may need a different treatment strategy.