What is bacterial vaginosis and what are its symptoms?

Bacterial vaginosis is a common vaginal infection caused by an imbalance in the intimate flora. This bacteriose affects 23 to 29% of women. Symptoms of vaginosis and treatment: our answers.

What is bacterial vaginosis?

Bacterial vaginosis is a common vaginal infection linked to an imbalance of the intimate flora. Protective lactobacilli decrease, and anaerobic bacteria, particularly Gardnerella vaginalis, Prevotella, or Mobiluncus, take their place.

A healthy vaginal microbiome relies on low bacterial diversity, dominated by lactobacilli. These bacteria produce lactic acid, which maintains an acidic vaginal pH (below 4.5). When this bacterial balance is disrupted, the pH rises, and pathogenic bacteria proliferate.

Bacterial vaginosis is not strictly a sexually transmitted infection. However, sexual activity plays a recognized role in its onset and recurrence, as confirmed by recent data published in the New England Journal of Medicine in March 2025.

Vaginosis, yeast infection, trichomoniasis: what are the differences?

Many women confuse these three vaginal infections. However, their causes, symptoms, and treatments differ significantly.

Criterion	Bacterial Vaginosis	Vaginal Yeast Infection	Trichomoniasis
Cause	Bacterial imbalance (anaerobes)	Candida albicans fungus	Trichomonas vaginalis parasite
Discharge	Grayish, thin, abundant	White, thick, cottage-cheese-like	Yellow-green, frothy
Odor	Fishy	Little to no odor	Unpleasant
Itching	Rare	Strong and typical	Moderate, burning sensation
STI Classification	No	No	Yes

This table is indicative only. Only a healthcare professional can make a reliable diagnosis based on a clinical examination and a vaginal swab.

What are the symptoms of bacterial vaginosis?

The most typical symptom of bacterial vaginosis remains a grayish vaginal discharge accompanied by a characteristic fishy odor. This odor often strengthens after sexual intercourse or during menstruation.

One fact often surprises affected women: nearly one in two cases of vaginosis is asymptomatic. You can have a bacterial imbalance without experiencing any clinical signs, which makes screening difficult without a vaginal swab.

The 6 symptoms of vaginosis to know

• Grayish or whitish vaginal discharge, thin and abundant, which stains underwear.
• Fishy vaginal odor, more pronounced after sexual intercourse or during menstruation.
• Slight irritation of the vulva, without the intense itching of a vaginal yeast infection.
• Burning sensation possible during urination, rarer than with cystitis.
• Vaginal pH above 4.5, measurable with test strips.
• Absence of redness or marked inflammation, which distinguishes vaginosis from vaginitis.

These signs can combine or appear in isolation. Faced with a persistent vaginal odor or unusual discharge, consulting a healthcare professional is the right approach.

What are the causes of bacterial vaginosis?

Bacterial vaginosis is caused by an imbalance in the vaginal flora. The exact origin of this imbalance is not fully understood, but several risk factors are documented.

Identified risk factors

• Vaginal douching: disrupts bacterial balance by eliminating protective lactobacilli.
• Unprotected sexual intercourse with one or more sexual partners.
• Recent change of partner, which alters the vaginal microbiota.
• Recent antibiotic therapy that destroys good bacteria in the flora.
• Intrauterine device (IUD) which promotes certain dysbiosis.
• Tobacco and unsuitable intimate hygiene products (perfumed soaps, irritating gels).
• History of vaginosis: one-third of women experience a recurrence within 3 months.

The role of the sexual partner: 2025 data

A study published in the New England Journal of Medicine in March 2025 by the StepUp team changed the understanding of bacterial vaginosis. Researchers showed that simultaneously treating the male partner significantly reduces the risk of recurrence in women in stable relationships.

This result challenges the common belief that vaginosis is not transmissible. Without reaching STI status, bacterial vaginosis is akin to a condition influenced by sexual activity. Couples' management becomes a serious avenue for reducing the recurrence rate.

How is bacterial vaginosis diagnosed?

The diagnosis of bacterial vaginosis relies on a medical consultation and a vaginal swab. Self-diagnosis remains unreliable, as symptoms are easily confused with those of a yeast infection or a sexually transmitted infection.

The doctor or gynecologist uses two validated methods: the Amsel criteria and the Nugent score.

Amsel's Criteria

Diagnosis is made if at least 3 of the following 4 criteria are met:

• Homogeneous, thin, grayish vaginal discharge.
• Vaginal pH greater than 4.5.
• Positive whiff test after adding potassium hydroxide.
• Presence of clue cells on microscopic examination.

Nugent Score

This reference method uses a Gram stain to evaluate bacterial populations in a vaginal sample. A score greater than or equal to 7 confirms bacterial vaginosis; between 4 and 6 indicates an intermediate flora.

What is the treatment for bacterial vaginosis?

The treatment for bacterial vaginosis primarily involves antibiotic therapy prescribed by a healthcare professional. The WHO updated its recommendations in 2024 in a guide dedicated to the management of bacterial vaginosis and STIs.

Reference antibiotic treatments

• Metronidazole orally (500 mg, twice daily for 7 days) or as a vaginal gel.
• Clindamycin as a vaginal cream for 7 days.
• Secnidazole as a single oral dose (2 g).

These medications are effective for the acute episode but do not, on their own, restore the vaginal flora. The recurrence rate at 6 months reaches 50% according to recent clinical data, which explains the growing interest in complementary approaches.

The benefit of probiotics as a complement

A meta-analysis of 35 randomized clinical trials, published by Abavisani et al. in the Taiwanese Journal of Obstetrics and Gynecology in 2024, confirmed that probiotics combined with antibiotics improve cure rates and reduce the risk of recurrence (OR: 0.34 for recurrence).

The most studied strains remain Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14, documented for over 20 years in scientific literature. They are thought to help rebalance the vaginal microbiota after antibiotic treatment.

How to prevent bacterial vaginosis and its recurrences?

Preventing bacterial vaginosis involves appropriate intimate hygiene and lifestyle habits that protect the vaginal microbiota. Several simple actions help reduce the risk of recurrence.

5 habits that protect your intimate flora

• Avoid vaginal douching: the vagina naturally self-cleans thanks to its acidic pH.
• Use a mild, unscented soap for external cleansing, not inside the vagina.
• Wear cotton underwear and avoid tight synthetic fabrics.
• Protect yourself during sexual intercourse, especially with a new partner.
• Support your flora with a diet rich in fiber and prebiotics.

A healthy lifestyle plays a direct role in the immune system and the balance of the vaginal microbiota. Smoking, chronic stress, and repeated antibiotic treatments disrupt this bacterial balance.

FAQ: Your questions about bacterial vaginosis

Is bacterial vaginosis an STI?

No. Bacterial vaginosis is not classified as a sexually transmitted infection. But 2025 data show that sexual activity influences its onset and recurrences, and a male partner can play a role in reinfection.

Can you have vaginosis without having had sex?

Yes. Women without sexual activity can develop bacterial vaginosis. The imbalance of the intimate flora can occur after antibiotic therapy, repeated vaginal douching, or hormonal variations during the menstrual cycle.

Does bacterial vaginosis go away on its own?

Sometimes yes, but without guarantee. Appropriate treatment prescribed by a doctor is still recommended to limit the risk of complications (pelvic inflammatory disease, increased risk of contracting an STI, complications during pregnancy).

What are the risks during pregnancy?

Untreated bacterial vaginosis in pregnant women increases the risk of premature birth, premature rupture of membranes, and miscarriage. Screening between 12 and 16 weeks is recommended for at-risk patients, even without symptoms.

Why does vaginosis return after treatment?

The recurrence rate reaches 50% at 6 months. Several causes: antibiotics also eliminate good bacteria, the sexual partner can reintroduce an imbalance, and certain habits (vaginal douching, smoking) maintain dysbiosis.

Is probiotic a treatment for vaginosis?

No, probiotics are not a medicine. They can be used to support the vaginal microbiota, in addition to prescribed medical treatment. Recent studies show an adjuvant effect on reducing recurrences.

When to consult a healthcare professional?

Consult as soon as unusual vaginal discharge, a persistent odor, itching, or abnormal bleeding appears. Early diagnosis avoids complications and allows for appropriate management.

Scientific sources

1. World Health Organization. Bacterial Vaginosis, fact sheet updated November 2024. who.int
2. Vodstrcil LA, Plummer EL, Fairley CK et al., StepUp Team. Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis. N Engl J Med. 2025 Mar 6;392(10):947-957. PubMed
3. Abavisani M, Sahebi S, Dadgar F et al. The role of probiotics as adjunct treatment in the prevention and management of gynecological infections: An updated meta-analysis of 35 RCT studies. Taiwan J Obstet Gynecol. 2024 May;63(3):357-368. PubMed
4. Lericolais C, Anastassiou A. Prévalence et facteurs de risques génitaux et sexuels de la vaginose bactérienne (étude DyvaM, Marseille), Thesis, Aix-Marseille University, 2023. DUMAS