Quick answer: Bacterial vaginosis (BV) happens when the normal balance of bacteria in the vagina shifts. Protective Lactobacillus bacteria decrease, and other bacteria, such as Gardnerella, overgrow. BV is the most common cause of abnormal vaginal discharge in women of reproductive age. It is not classed as a sexually transmitted infection, but it is linked to sexual activity, new or multiple partners, and douching. The most common symptom is a thin, grayish-white discharge with a fishy odor, though many women have no symptoms at all. BV is diagnosed by a clinician and is usually treated with prescription antibiotics.
BV is very common, and it is nothing to be embarrassed about. Understanding why it happens can help you spot the signs early, get the right care, and build habits that support your vaginal health afterward.
What happens in the vagina when BV develops
A healthy vagina is usually dominated by Lactobacillus bacteria. These bacteria produce lactic acid, which helps keep the vaginal environment acidic, typically around pH 3.8 to 4.5. This acidity helps limit the growth of less helpful microbes.
In BV, the number of Lactobacillus bacteria falls and a mix of other bacteria, including Gardnerella vaginalis, Prevotella, and others, becomes dominant. The vaginal pH rises above 4.5, and these bacteria produce compounds that cause the characteristic fishy odor.
| Balanced vaginal microbiome | Bacterial vaginosis | |
|---|---|---|
| Main bacteria | Lactobacillus species | Gardnerella and other mixed bacteria |
| Vaginal pH | Usually 3.8 to 4.5 | Above 4.5 |
| Discharge | Clear to white, varies across your cycle | Thin, gray or off-white, often watery |
| Odor | Mild or none | Fishy, often stronger after sex |
What causes bacterial vaginosis?
Researchers do not fully understand why BV develops in some women and not others. It is best understood as a shift in the vaginal microbiome rather than an infection caught from one source. Several factors are linked to that shift:
Sexual activity
BV is more common in women who are sexually active, especially with a new partner or multiple partners. Semen is naturally alkaline, which can temporarily raise vaginal pH. BV is not considered an STI, but sexual activity is clearly linked to it, and it can also occur between female partners. Read more in fishy smell after sex: why it happens.
Douching and internal washing
Douching and washing inside the vagina can wash away protective bacteria and are consistently linked to a higher risk of BV. The vagina is self-cleaning and does not need internal washing.
Menstruation and hormonal changes
Menstrual blood has a higher pH than the vagina, and hormonal shifts across the cycle can affect the vaginal environment. Some women notice symptoms around their period.
Other factors
Smoking, recent antibiotic use, and an intrauterine device (IUD) have also been associated with BV in some studies. Having had BV before increases the chance of it returning.
Good to know: You cannot get BV from toilet seats, swimming pools, or bedding. Women who have never had sex rarely get it, but it can happen.
Risk factors at a glance
- A new sexual partner or multiple sexual partners
- Douching or using internal cleansing products
- Sex without condoms
- Smoking
- A previous episode of BV
- Low levels of Lactobacillus bacteria
Symptoms of bacterial vaginosis
Many women with BV have no symptoms. When symptoms do appear, they may include:
- Thin, watery discharge that is grayish-white or off-white
- A fishy odor, often more noticeable after sex or during your period
- Mild itching or irritation around the vagina, although significant itching is more typical of a yeast infection
- Burning when urinating, in some cases
These symptoms overlap with other conditions, including yeast infections, trichomoniasis, and irritation from products. That is why testing matters. Read more in our guide to BV or yeast infection: how to spot the difference and BV vs. trich.
Why BV should not be ignored
BV sometimes clears on its own, but it is worth getting checked. Untreated BV is associated with:
- A higher risk of getting sexually transmitted infections, including HIV, if exposed
- Complications in pregnancy, such as preterm birth
- A higher risk of pelvic infection after some gynecological procedures
How BV is diagnosed and treated
A clinician can diagnose BV using your symptoms, an examination, a vaginal pH test, and a look at a sample of discharge under a microscope or a lab test. Home pH tests can show that pH is raised, but they cannot confirm BV on their own.
BV is usually treated with prescription antibiotics, either as tablets or as a vaginal gel or cream. Take the full course, even if symptoms improve. BV commonly returns, so if symptoms come back, see your clinician again rather than repeating self-treatment. Recent research suggests that treating male partners may reduce recurrence for some couples, so ask your clinician whether this applies to you.
Supporting your vaginal balance after treatment
Once BV has been diagnosed and treated, these habits support a healthy vaginal environment:
- Do not douche or wash inside the vagina. Rinse the external vulva with lukewarm water.
- Avoid harsh external scented washes, perfumed douches, and strong deodorizing sprays.
- Use condoms, especially with a new partner.
- Change out of damp swimwear or workout clothes promptly.
- Consider a microbiome-conscious routine that supports Lactobacillus. See how long to use vaginal probiotics.
How VagiBiom® fits into a balanced routine
VagiBiom® Vaginal Probiotic Suppository is formulated with a patented probiotics-prebiotics complex and hyaluronic acid, designed to support a Lactobacillus-friendly vaginal environment, moisture, and everyday comfort. Many women use it as part of their routine after completing clinician-directed treatment. VFlora®, a vegan Lactobacillus crispatus suppository, is another option designed to help nourish and maintain healthy vaginal flora.
| Designed to support | Not designed to do |
|---|---|
| A microbiome-conscious vaginal-care routine | Diagnose or treat BV, a yeast infection, or an STI |
| Vaginal moisture and comfort when used as directed | Replace antibiotics prescribed for BV |
| Lactobacillus-friendly care after treatment | Guarantee that BV will not return |
Shop Vaginal Probiotic Suppositories
Subscribe and save 10% with monthly delivery to keep your routine consistent.
When to see a doctor
Make an appointment if you have:
- A new, fishy, or otherwise unusual vaginal odor
- Gray, green, yellow, or unusually heavy discharge
- Symptoms that return after treatment
- Pelvic pain, fever, or bleeding outside your period
- Symptoms during pregnancy, or a chance you may be pregnant
- A new sexual partner or concern about an STI
Frequently asked questions
Is bacterial vaginosis a sexually transmitted infection?
No. BV is not classed as an STI, but it is linked to sexual activity, and having BV can increase your risk of getting an STI if you are exposed.
What is the main cause of bacterial vaginosis?
BV is caused by a shift in vaginal bacteria, where protective Lactobacillus decreases and other bacteria overgrow. Sexual activity, new partners, and douching are among the strongest linked factors.
Can BV go away on its own?
It sometimes does, but it can also persist or return. Because untreated BV is linked to health risks, it is best to see a clinician for diagnosis and treatment.
Why does BV smell worse after sex?
Semen is alkaline. When it mixes with vaginal fluid during BV, it can release more of the compounds that cause the fishy odor.
Why does my BV keep coming back?
BV commonly recurs. Ongoing risk factors, an untreated partner, or a microbiome that has not re-established Lactobacillus can all play a role. See your clinician to discuss a longer-term plan.
Can probiotics treat BV?
Probiotics are not a replacement for prescribed treatment. They can be part of a microbiome-conscious routine after treatment, used as directed.
Can I prevent BV?
No method guarantees prevention, but avoiding douching, using condoms, and supporting a healthy vaginal environment may lower your risk.