Bacterial vaginosis (BV) is a vaginal condition that happens when there’s an imbalance of the natural bacteria in your vagina. But what causes bacterial vaginosis, exactly?

Although the exact cause isn’t fully understood, research has identified a few risk factors that can make you more prone to developing bacterial vaginosis. 

Keep reading to learn more, including how to treat and diagnose bacterial vaginosis.

What is bacterial vaginosis? 

Bacterial vaginosis is a common vaginal infection caused by an imbalance of the healthy bacteria in your vagina. It’s one of the top causes of abnormal vaginal discharge and vaginal odor, and affects almost 30% of women aged 15-44 each year, according to the Centers for Disease Control (CDC).

Normally, the vaginal microbiome is home to a good mix of bacteria, with Lactobacilli bacteria being the predominant and good bacteria.

Lactobacilli keep the vaginal pH slightly acidic, which stops harmful bacteria from growing. But in BV, the Lactobacillus population decreases, and other anaerobic bacteria take over.

Bacteria linked to bacterial vaginosis include:

Symptoms of bacterial vaginosis

The most common bacterial vaginosis symptoms are: 

Rarely, vaginal itching or irritation and a burning sensation when you pee.

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What causes BV?

The main cause of bacterial vaginosis is the disruption of the balance between beneficial and harmful bacteria in the vagina. What causes this imbalance? Researchers are still trying to figure out the ins and outs, but there are some known risk factors for bacterial vaginosis.

Sex

Bacterial vaginosis isn’t considered a sexually transmitted infection (STI) because you can get bacterial vaginosis even if you’re not sexually active. However, it can be transmitted through sex — confusing, we know. 

Being sexually active is a risk factor for bacterial vaginosis for a few reasons. Firstly, sex can introduce new bacteria into the vagina, disrupting the natural balance of the vaginal flora. Additionally, semen’s slightly alkaline pH can raise the vaginal pH and throw the vaginal flora off-kilter.

Using shared sex toys without proper cleaning can also contribute to the spread of bacteria that cause bacterial vaginosis.

Having a new sex partner or multiple sex partners (whether they’re male or female) can increase the risk of bacterial vaginosis. 

Vaginal douching

Women who douche regularly are at a higher risk of developing bacterial vaginosis. Douching (the practice of cleaning the vagina with water or other fluids) can disturb the natural bacterial balance. Although many people think it can treat symptoms like abnormal vaginal discharge, it actually washes away good bacteria, making symptoms worse.

The vagina is a self-cleaning organ (vaginal discharge is proof of that), so douching is useless at best and harmful at worst. 

Hormonal changes

Hormonal fluctuations during your period, pregnancy, or menopause can alter the vaginal environment, making it more susceptible to bacterial imbalances and infections like bacterial vaginosis.

Estrogen helps produce a sugar called glycogen, which thickens the lining of the vagina and acts as a food source for lactobacilli. When estrogen levels are low — like in menopause or certain phases of the menstrual cycle — there is less glycogen, resulting in fewer Lactobacilli to maintain a healthy vaginal pH and keep “bad” bacteria in check. This can create an opportunity for harmful bacteria in your vagina to grow.

Antibiotics

Although they can kill harmful bacteria, some antibiotics can also deplete beneficial bacteria in the vagina, leading to an imbalance and increasing your risk of bacterial vaginosis.

“But isn’t bacterial vaginosis treated with antibiotics?” Yes, however not all antibiotics are created equal, nor do they all target the same bacteria. Recent use of antibiotics for an unrelated bacterial infection could affect your vaginal microbiome, giving BV-associated bacteria a chance to take over.

Lifestyle

Other factors, including smoking, chronic stress, and having a weakened immune system can also influence the vaginal flora and increase the risk of bacterial vaginosis. It’s unclear exactly what the link is here, so we need more research on how these factors can increase your risk of bacterial vaginosis.

Bacterial vaginosis diagnosis

Two common methods are used to diagnose bacterial vaginosis. The first method involves looking for specific symptoms, known as the Amsel criteria:

  • abnormal vaginal discharge
  • clue cells
  • high pH
  • a fishy smell.

The second method (called the Nugent score) is more specific and involves examining vaginal fluid under a microscope to check for different types of bacteria. Based on the quantity of each type, a score is assigned to indicate the bacterial diversity in the sample. A score under four is considered healthy, 4-7 is intermediate, and 7-10 indicates high diversity, which corresponds to bacterial vaginosis.

Bacterial vaginosis treatment

To treat bacterial vaginosis, a healthcare provider will prescribe you antibiotics:

  • Oral antibiotics: Metronidazole, tinidazole, secnidazole, or clindamycin pills.
  • Intra-vaginal antibiotics: Metronidazole gel or clindamycin cream or pessary applied directly into the vagina.

Completing the full course of antibiotics is essential, even if symptoms improve before the medication is finished, to ensure the infection is fully treated.

Bacterial vaginosis also has a nasty reputation for being stubborn, so recurrent bacterial vaginosis is really common. Although antibiotics are an effective treatment, the infection can come back within 3 to 6 months after proper treatment. 

As frustrating as that is, it’s really important to treat BV. Untreated bacterial vaginosis can cause serious complications and is linked with a higher risk of:

Preventive measures can help reduce the risk of developing bacterial vaginosis. Here are some tips to prevent bacterial vaginosis and generally look after your vaginal health:

  • Avoid douching: Remember, your vagina is self-cleaning, and using douches or vaginal deodorants upsets the normal balance of vaginal bacteria.
  • Practice safe sex: Use condoms or a dental dam during sex, cover sex toys with a condom, and ensure they’re cleaned thoroughly after each use.
  • Maintain proper hygiene: Use mild, unscented soaps to clean the vulva, and change your period products regularly.
  • Stop smoking: smoking is bad for your health for myriad reasons, and an increased risk of bacterial vaginosis is just one of them.
  • Take a vaginal microbiome test: bacterial vaginosis often doesn’t cause symptoms. Evvy’s vaginal microbiome test can screen for over 700 species of bacteria, whether you have recurrent symptoms or not. If eligible, you’ll receive a custom plan based on your results and optional prescription treatment.

When to see a healthcare provider

Bacterial vaginosis is by no means the only cause of unusual vaginal discharge. Many vaginal infections and sexually transmitted infections can cause symptoms similar to bacterial vaginosis, so it’s important to seek medical care if you experience abnormal vaginal discharge, along with symptoms such as a fishy smell, vaginal itching, a burning sensation, or pain when you pee or have sex.

FAQ

What is the main cause of BV?

Bacterial vaginosis is caused by a change in the natural balance of bacteria in your vagina. The exact cause isn't fully understood, but it's more common in sexually active women (although it's not an STI because women who haven't had sex can also get it). Having a new sex partner or multiple sex partners, douching, and not using condoms can increase your risk of getting bacterial vaginosis.

How is bacterial vaginosis transmitted?

Sex is the biggest risk factor for bacterial vaginosis because bacteria can be passed on during sex, including oral sex or by sharing sex toys. Semen can also increase the vaginal pH and alter your normal balance. That said, you can get bacterial vaginosis even if you're not sexually active. Your period, smoking cigarettes, and using douches can all make you more likely to develop bacterial vaginosis. 

Can you get BV from a man? 

Yes. Although men can’t get bacterial vaginosis, they can carry bacteria linked with bacterial vaginosis on their penis and in their sperm, and pass them on during sex. Plus, semen has a slightly alkaline pH, which can impact vaginal bacteria.