Bacterial vaginosis: how to recognize it, treat it, and prevent it from coming back

An odor you notice at the end of the day, discharge that is more watery and grayer than usual, and that particular discomfort that makes you want to wash more rather than talk about it.

Bacterial vaginosis is the most common cause of vaginal discharge among women of reproductive age, according to the World Health Organization. It does not come from a germ picked up somewhere: it is an imbalance of the vaginal flora, in which protective lactobacilli give way to other bacteria. It is easily treated within a few days with an antibiotic. The real issue, and the one discussed less often, is that it returns very frequently.

Here is how to recognize it, how it differs from a yeast infection, how it is treated, and what the latest research says about recurrences.

What is bacterial vaginosis?

An imbalance, not an infection

The vagina is permanently home to a population of bacteria, dominated by lactobacilli. The French National Health Insurance service describes this flora as being made up of nonpathogenic bacteria that protect against colonization of the vagina by pathogens. By producing lactic acid, lactobacilli maintain an acidic environment in which other bacteria have difficulty proliferating.

Bacterial vaginosis occurs when this balance shifts. The MSD Manual refers to dysbiosis, a complex alteration of the vaginal flora: lactobacilli decrease, and anaerobic bacteria take their place, with their concentration increasing tenfold to one hundredfold.

This is the nuance that makes all the difference in how one experiences the diagnosis. There is nothing you have caught and nothing to reproach yourself for when it comes to hygiene. An imbalance in the vaginal microbiome is common, and the body often corrects it on its own. If the terminology is unclear, our glossary of the female reproductive system puts each organ in its proper place.

The bacteria involved

Several species are found together, not just one. The MSD Manual lists Prevotella, Peptostreptococcus, Gardnerella vaginalis, Mobiluncus, and Mycoplasma hominis.

Gardnerella vaginalis is the best-known species, to the point that people sometimes refer to a “Gardnerella infection” as though it were a single microbe responsible for everything. This is inaccurate: the bacterium is present in many women without causing any symptoms, and it is its overgrowth in the context of depleted vaginal flora that causes the problem, not its mere presence.

A very common condition

The WHO states that bacterial vaginosis is the most common cause of vaginal discharge among women of reproductive age, with prevalence ranging from 23 to 29% depending on the country and population group. The MSD Manual, for its part, describes it as the most common infectious vaginitis.

In other words, it is neither a rare condition nor a sign of neglect. It is one of the most common reasons to consult a healthcare professional about unusual white discharge.

Symptoms of bacterial vaginosis

Gray discharge and a characteristic odor

The typical picture is fairly recognizable. The MSD Manual describes a thin, foul-smelling yellow-green or gray discharge, usually with a fishy odor. The French National Health Insurance service, discussing bacterial vaginosis, refers to fluid, abundant, grayish or yellowish, foul-smelling discharge.

Odor is the most commonly reported symptom, and the most difficult to live with on a daily basis. It is explained by compounds produced by anaerobic bacteria, which are released all the more as the environment becomes alkaline. This is exactly the principle behind the potassium hydroxide test used during consultations, and the same mechanism occurs after intercourse or during menstruation, two situations that raise vaginal pH. Many women in fact notice this odor first at these times, which has nothing to do with the idea that menstrual blood is dirty. A bothersome odor during menstruation is not necessarily a sign of an infection.

What is missing, and is precisely what gives it away

Here is the most useful point in this entire article. In bacterial vaginosis, the MSD Manual states that itching, irritation, erythema, and edema are not common. No itching, no red and swollen vulva, no marked burning.

This is what most clearly sets it apart from a yeast infection, where itching is prominent. However, the WHO mentions itching and burning among the possible signs: they can occur, they are simply not the rule. When they dominate the picture, think of something else, or of two problems occurring at the same time.

One woman in two feels nothing

A literature review published by Coudray and Madhivanan indicates that about 50% of cases of bacterial vaginosis are asymptomatic. It is then discovered by chance, during a Pap smear or a sample taken for another reason.

This figure has a practical consequence: the absence of symptoms does not guarantee a balanced vaginal flora, and conversely, discharge that changes in appearance warrants medical advice even if nothing itches or burns.

Bacterial vaginosis, yeast infection, or STI: the difference

The chart that distinguishes them

This is the number-one source of confusion, and it comes at a cost: weeks lost treating the wrong thing.

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Why the pharmacy antifungal treatment does not work

An over-the-counter antifungal vaginal suppository acts on a fungus, Candida albicans in the vast majority of cases. Bacterial vaginosis is caused by bacteria. The treatment therefore has no reason to work, and the only result is an additional delay before receiving the right care.

If you have had a vaginal yeast infection before and recognize “the same thing,” be wary of that impression: the two may look similar from a distance, but they are treated very differently. The useful thing to check is the odor and itching, the two criteria that best distinguish the two conditions.

A third possibility is sometimes overlooked: the French national health insurance service lists vaginal dryness and intolerance to a product among the possible causes of vaginitis, alongside infections. Persistent discomfort is therefore not necessarily microbial.

Causes and risk factors

What weakens lactobacilli

There is no single cause. What matters is anything that weakens the population of lactobacilli or raises the vaginal pH.

The MSD Manual identifies multiple sexual partners, sharing sex toys, inconsistent condom use, and the presence of an intrauterine device as risk factors. It adds an important point: bacterial vaginosis can occur in women who have never had vaginal intercourse. The WHO, for its part, cites douching, unprotected sex with one or more partners, and intravaginal practices involving the insertion of herbs or products into the vagina.

The French national health insurance service also lists, for vaginitis in general, synthetic and tight-fitting underwear, excessive hygiene with irritating products, sexual intercourse, and taking antibiotics, which destroy part of the protective flora. If you wear an IUD, this is not a reason to have it removed: it is simply something to mention during your consultation.

Finally, intimate discomfort does not have the same cause at every age. After menopause, dryness and discomfort are often due to something other than bacterial vaginosis and warrant specific medical advice rather than a treatment taken at random.

Vaginal douching, the most avoidable factor

How the diagnosis is made

The examination and Amsel criteria

The diagnosis is made during a consultation by combining the appearance of the discharge with a few simple tests. The MSD Manual uses the Amsel criteria: three of the following four must be present.

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The WHO mentions the same tools: fresh-mount microscopy, Gram staining of the vaginal smear, pH measurement, and the whiff test. A laboratory sample can complete the assessment; Assurance Maladie specifies that a self-collected or clinician-collected sample allows bacteriological, parasitological, and mycological analyses.

What not to do before the consultation

This is practical advice that is rarely given. Assurance Maladie recommends avoiding intimate washing before the consultation: the secretions are what the doctor needs to examine, and washing them away means erasing the main diagnostic clue.

Similarly, local treatment started the day before can distort the results. It is better to arrive without having tried anything.

Treatments for bacterial vaginosis

Prescribed antibiotics

Treatment is simple, short, and effective. It involves antibiotics active against anaerobic bacteria, taken orally or applied locally. Here are the regimens indicated by the MSD Manual.

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These regimens are provided for information only: the doctor chooses the treatment based on your situation. Assurance Maladie lists the same drugs for bacterial vaginal infections, notably secnidazole or metronidazole. For pregnant women, the MSD Manual states that topical regimens are preferred.

Instructions during treatment

• No alcohol with metronidazole. The summary of product characteristics for FLAGYL 500 mg states that concomitant use of metronidazole and alcohol is discouraged, with a disulfiram-like reaction described as warmth, flushing, vomiting, and tachycardia. This also applies to medicines containing alcohol.
• Sexual intercourse. Assurance Maladie advises abstaining from sexual intercourse or using a condom throughout treatment for vaginitis.
• Hygiene. Wash externally only twice a day, using a gentle product.
• Finish the entire pack, even if the odor has disappeared after two days. Stopping treatment early encourages recurrence.

Should it be treated when there are no symptoms

The question arises given the proportion of asymptomatic cases. In everyday practice, it is the discomfort experienced that prompts treatment. Two situations are exceptions and require specific medical advice: pregnancy, given the obstetric complications described below, and the period before a gynecological procedure, because of the risk of infection.

Is bacterial vaginosis contagious

It is not an STI in the strict sense

No, bacterial vaginosis is not classified as a sexually transmitted infection. The argument is sound: the MSD Manual states that it can occur in women who have never had vaginal intercourse. It is not an agent transmitted from one person to another, but an ecosystem that becomes unbalanced.

That said, sexual activity clearly plays a role, since the number of partners and inconsistent condom use are among the risk factors. The most accurate way to put it is therefore: it is not an STI, but neither is it independent of sexual activity. The WHO also points out that bacterial vaginosis increases the risk of contracting other STIs, making condoms all the more useful, including when choosing to have sex during your period. For genuinely transmissible infections, our article on genital herpes describes a very different case.

What the study published in 2025 changes

The traditional position is clear. The MSD Manual states that treatment of sexual partners is not recommended, and Assurance Maladie provides for partner treatment only for vaginitis considered an STI, such as Trichomonas or Chlamydia, for example.

A randomized trial published in March 2025 in the New England Journal of Medicine seriously calls this position into question. The StepUp study followed 164 monogamous heterosexual couples in which the woman had symptomatic bacterial vaginosis. In one group, only the woman was treated. In the other, the male partner additionally received oral metronidazole for 7 days and 2% clindamycin cream for topical application.

Why bacterial vaginosis returns so often

A high recurrence rate

This is the most discouraging aspect of the subject, and it is better to know it from the outset than to discover it after the third episode. The MSD Manual notes that bacterial vaginosis frequently recurs. The literature review by Coudray and Madhivanan cites Bradshaw's research, which reports a 58% recurrence rate within one year of treatment, as well as rates of 30 to 40% within three months.

In other words, a recurrence is not a personal failure or proof that you did something wrong. It is the usual behavior of this condition, and it is far from the only one to work this way: urinary tract infections follow a comparable pattern of recurrence.

What drives recurrence

The mechanism is logical. The antibiotic eliminates the excess bacteria, but it does not restore the population of lactobacilli. As long as the protective flora has not reclaimed its place, the conditions remain favorable for the imbalance to return.

• Persistence of the initial contributing factors: vaginal douching, harsh hygiene products, unprotected sex with a new partner.
• A shortened course of treatment as soon as the odor disappears.
• Recolonization from a partner, a hypothesis that the StepUp trial makes considerably more credible than before.
• Repeated courses of antibiotics for other reasons, which weaken the vaginal flora each time.

In the event of repeated recurrences, prolonged treatment regimens and approaches aimed at restoring the vaginal flora are available. These should be discussed with a doctor or gynecologist, not at a pharmacy or on a forum.

The risks of untreated bacterial vaginosis

The risk of infection

In most cases, untreated bacterial vaginosis does not progress to a serious illness. However, it weakens a natural barrier, and this has measurable consequences.

• An increased risk of contracting HIV and other STIs, as mentioned by the WHO.
• Pelvic inflammation. The MSD Manual cites an increased risk of pelvic inflammatory disease and endometritis.
• An increased risk of infection after a gynecological procedure, which explains why it is treated before certain procedures.

During pregnancy

This is the situation in which the issue becomes genuinely serious and which warrants seeking medical advice without delay.

Also seek medical advice promptly if you have a fever, pelvic pain, bleeding outside your period, or blood-tinged discharge. These signs are not typical of simple bacterial vaginosis and may point to something else, as we explain in our articles on bleeding outside your period and spotting.

Preventing bacterial vaginosis every day

Recommendations from the French National Health Insurance

The French National Health Insurance's vaginitis prevention page provides a short, practical list. Here it is, focused on what affects the balance of the vaginal flora.

• Do not wash your intimate area more than once or twice a day. Any more than that can damage the skin.
• Use a mild, fragrance-free soap or a gentle intimate hygiene product, and do not use foaming antiseptics.
• Never clean inside the vagina, and avoid vaginal douches in particular.
• Dry the vulva thoroughly after each wash, and wipe from front to back after using the toilet.
• Choose cotton underwear over synthetic fabrics, and avoid wearing overly tight clothing.
• Avoid staying in wet underwear, including a swimsuit.
• Change your tampon or period product frequently during your period. For guidance on the actual lifespan of an internal product, our article on a tampon's life cycle provides useful benchmarks.
• Use a condom during every sexual encounter.

Two of them come up particularly often when discussing period products: changing regularly and not staying in damp underwear. Our guide to choosing the right period product compares the options one by one, while the article on toxic shock syndrome explains why wearing time matters for internal products.

Underwear: a detail that matters

The recommendation about cotton is explicit and comes from an official source, not a magazine tip. It is also one of the few things we can do every day without any effort.

At Smoon, the cotton range was designed exactly around this principle: what touches the skin is GOTS-certified organic cotton, while the technical layers remain inside. It is tested under gynecological supervision, validated by a clinical study, and certified PFAS-free. The rest of the range uses microfiber, and our menstrual underwear comparison guide explains how each material affects everyday use.

One final practical point. Many women wear a disposable panty liner every day because of discharge they find bothersome. A washable pair of underwear changed daily serves the same purpose, without the layer of plastic, and can be washed in cold water. That's the idea behind underwear for light daily discharge, and caring for period underwear is simpler than it may seem. As a reminder, discharge occurs all year round and varies throughout the cycle: cervical mucus changes in appearance as ovulation approaches, and this is not a sign of infection. All our briefs are also available in microfiber in the period underwear collection if cotton is not what you're looking for.

Frequently asked questions about bacterial vaginosis

• 01What is bacterial vaginosis?

  It is an imbalance of the vaginal flora, not an infection caught from outside. Protective lactobacilli decrease while anaerobic bacteria multiply, including Gardnerella vaginalis, Prevotella, Peptostreptococcus, Mobiluncus, and Mycoplasma hominis. The MSD Manual describes it as dysbiosis, a complex change in the vaginal flora. The WHO identifies it as the most common cause of vaginal discharge in women of reproductive age, with a prevalence of between 23 and 29%.

• 02What are the typical symptoms of bacterial vaginosis?

  Thin, abundant, grayish or yellowish discharge with a pronounced odor, often described as fishy. The MSD Manual specifies that itching, irritation, erythema, and edema are uncommon: this is what most clearly distinguishes bacterial vaginosis from a yeast infection. About half of cases cause no symptoms.

• 03How can you tell the difference between bacterial vaginosis and a yeast infection?

  Two criteria clearly distinguish the two conditions. Bacterial vaginosis causes thin, grayish discharge with a pronounced odor and little or no itching. A yeast infection causes whitish, thick discharge resembling curdled milk, with itching and burning sensations as the main symptoms and little odor. The treatments are completely different: antibiotics for bacterial vaginosis and antifungals for a yeast infection. An over-the-counter antifungal does not treat bacterial vaginosis.

• 04How is bacterial vaginosis diagnosed?

  Diagnosis is based on the Amsel criteria, three of which must be present: yellow-green or gray discharge, a vaginal fluid pH above 4.5, a fishy odor on the potassium hydroxide whiff test, and the presence of clue cells on microscopic examination. A laboratory sample may supplement the assessment. Practical advice from Assurance Maladie: avoid washing your intimate area before the appointment, because the discharge is what the doctor needs to examine.

• 05What treatment is effective against bacterial vaginosis?

  A prescription antibiotic. The MSD Manual lists oral metronidazole 500 mg twice daily for 7 days, 0.75% metronidazole vaginal gel at 5 g per day for 5 days, 2% clindamycin vaginal cream once daily for 7 days, and secnidazole 2 g as a single dose. For pregnant women, topical regimens are preferred. The summary of product characteristics for FLAGYL 500 mg advises against the concomitant use of metronidazole and alcohol because of a disulfiram-like reaction.

• 06Is bacterial vaginosis contagious or sexually transmitted?

  It is not a sexually transmitted infection in the strict sense. The MSD Manual indicates that it can occur in women who have never had vaginal intercourse. Sexual activity nevertheless plays a role, since the number of partners and inconsistent condom use are among the risk factors. The WHO also points out that bacterial vaginosis increases the risk of contracting other STIs, including HIV.

• 07Should a partner be treated in cases of bacterial vaginosis?

  The conventional position is no: the MSD Manual states that treating sexual partners is not recommended, and Assurance Maladie only provides for it in the case of vaginitis considered an STI. A randomized trial published in March 2025 in the New England Journal of Medicine qualifies this position. Among 164 monogamous heterosexual couples, bacterial vaginosis had recurred after 12 weeks in 35% of women whose partners had been treated, compared with 63% in the group receiving usual care. This is not yet an official recommendation in France, but it is worth discussing in cases of repeated recurrences.

• 08Why does bacterial vaginosis keep coming back?

  Because antibiotics eliminate the excess bacteria but do not restore the lactobacillus population, leaving conditions favorable for the imbalance to return. The figures are high: a literature review citing Bradshaw's research reports a 58% recurrence rate within one year after treatment, and 30% to 40% within three months. A recurrence is therefore not a personal failure. In cases of repeated recurrences, longer treatment regimens are available and should be discussed with a doctor.

• 09What are the risks if bacterial vaginosis is left untreated?

  Outside pregnancy, untreated bacterial vaginosis generally does not progress to a serious illness, but it weakens a protective barrier. The WHO mentions an increased risk of contracting HIV and other STIs, as well as pelvic inflammation. The MSD Manual cites an increased risk of pelvic inflammatory disease and endometritis. During pregnancy, it cites a risk of chorioamnionitis, premature rupture of the membranes, preterm labor, and premature birth.

• 10How can bacterial vaginosis be prevented on a daily basis?

  L'Assurance Maladie recommends limiting intimate washing to once or twice a day, using a mild, fragrance-free soap, never cleaning inside the vagina, and especially avoiding vaginal douching. It also recommends drying the vulva thoroughly, choosing cotton underwear over synthetic fabrics, avoiding overly tight clothing, not staying in wet underwear, changing menstrual protection frequently, and using a condom every time you have sex. The WHO likewise emphasizes stopping vaginal douching and intravaginal practices.