Bacterial Vaginosis
Symptoms, Causes & Treatment
Understanding bacterial vaginosis: what it is, what causes it, how to tell it apart from thrush and STIs, and the effective treatments available including online prescriptions.
What Is Bacterial Vaginosis (BV)?
Bacterial vaginosis (BV) is the most common cause of abnormal vaginal discharge in women of reproductive age. It is caused by a disruption in the normal vaginal flora -- specifically, a reduction in protective Lactobacillus bacteria and an overgrowth of mixed anaerobic bacteria, including Gardnerella vaginalis, Atopobium vaginae, Prevotella species, and Mobiluncus species.
A healthy vagina is dominated by Lactobacillus species, which produce lactic acid and maintain an acidic vaginal pH (3.8–4.5). This acidic environment inhibits the growth of potentially harmful organisms. In BV, the Lactobacillus population is depleted, the pH rises above 4.5, and anaerobic bacteria proliferate, producing the characteristic symptoms.
BV is extremely common. Studies estimate that 12–30% of women of reproductive age are affected at any given time, though up to half of these women have no symptoms at all and the condition is detected incidentally.
BV is not a sexually transmitted infection (STI). It occurs in women who have never been sexually active, though it is more common in sexually active women and is associated with certain sexual behaviours. Male sexual partners do not require treatment, as treating male partners has not been shown to reduce recurrence.
What Are the Symptoms of Bacterial Vaginosis?
BV has a characteristic presentation that differs from thrush and from STIs. Getting the right diagnosis is essential for appropriate treatment.
Thin, greyish-white or off-white vaginal discharge · Strong fishy odour, often worse after sex · No significant itch or soreness (BV is typically not irritating) · Increased discharge volume
BV with pelvic pain or fever — possible ascending infection (PID) · BV in pregnancy — associated with preterm birth; always treat · Recurrent BV (3 or more episodes in a year) — may require specialist review and extended antibiotic treatment
BV in pregnancy is associated with preterm birth and requires prompt treatment. Seek assessment if you are pregnant and have any unusual vaginal discharge. BV with pelvic pain or fever may indicate PID — seek same-day assessment.
What Causes Bacterial Vaginosis?
BV is not caused by poor hygiene — it is caused by an imbalance in vaginal bacteria. Certain factors disrupt the normal Lactobacillus-dominant environment and allow anaerobic bacteria to overgrow.
BV results from overgrowth of anaerobes including Gardnerella vaginalis. It is associated with new sexual partners, douching, and use of perfumed products that disrupt vaginal pH.
BV is not sexually transmitted but is more prevalent in sexually active women and those with multiple partners. Semen exposure and new partners alter vaginal pH, predisposing to BV.
A single course of metronidazole clears BV in up to 80% of women, but recurrence is extremely common — around 50% of women relapse within 3 months. This is not treatment failure but reflects the chronic nature of vaginal dysbiosis.
Hormonal fluctuations during the menstrual cycle and pregnancy alter vaginal pH and Lactobacillus colonisation, making BV more common in the luteal phase and during pregnancy.
Smoking is strongly and independently associated with BV. Tobacco reduces vaginal Lactobacillus populations and promotes growth of BV-associated anaerobes through mechanisms not yet fully understood.
Intrauterine devices (IUDs), particularly copper IUDs, are associated with slightly higher BV rates. Scented tampons, vaginal sprays, and bubble baths all disrupt normal vaginal ecology.
Key Risk Factors
How Is Bacterial Vaginosis Diagnosed?
BV can often be diagnosed on clinical grounds: thin grey-white discharge with a fishy odour and absence of itch/soreness. pH testing (>4.5) and a high vaginal swab (showing clue cells) confirm the diagnosis. A negative Whiff test (no odour on adding KOH to discharge) does not exclude BV.
How Is Bacterial Vaginosis Treated?
Metronidazole (antibiotic) is the first-line treatment for BV, available as oral tablets or vaginal gel. Clindamycin vaginal cream is an alternative for those intolerant of metronidazole.
Supportive Measures
Complete the full antibiotic course — stopping early increases recurrence risk. Avoid alcohol during oral metronidazole treatment. Do not use perfumed products in or around the vagina. Use condoms to reduce semen-induced vaginal pH changes. Probiotic supplements (Lactobacillus strains) taken after antibiotic treatment may help restore protective flora.
Recurrent Bacterial Vaginosis
Recurrent BV (3 or more episodes per year) is common and challenging. Extended antibiotic courses, intravaginal boric acid suppositories (off-label), and twice-weekly metronidazole gel maintenance therapy all have evidence for recurrence reduction. Probiotic Lactobacillus supplements may help. Specialist referral to a sexual health or gynaecology clinic is appropriate for women with frequent recurrences.
When Should You Seek Medical Advice?
BV with fever and severe pelvic pain may indicate ascending infection (pelvic inflammatory disease). Seek same-day emergency assessment.
You have unusual vaginal discharge and are pregnant · You have had BV 3 or more times in the past year · You have vaginal symptoms alongside pelvic pain · You have had a new sexual partner and have new vaginal symptoms.
How to Reduce BV Recurrence
BV can be reduced but not always prevented. These evidence-based measures support healthy vaginal flora.
Avoid vaginal douching, which disrupts vaginal flora and strongly predisposes to BV. The vagina is self-cleaning — no internal washing is needed or beneficial.
Consistent condom use reduces BV recurrence risk by limiting exposure to semen, which raises vaginal pH. Condoms also prevent STIs that cause abnormal discharge.
Boric acid vaginal suppositories (600mg nightly for 2 weeks) have strong evidence for recurrent BV that has not responded to standard antibiotics. Available from specialist pharmacies; not for use in pregnancy.
Probiotic capsules containing Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 taken orally or vaginally have evidence for reducing BV recurrence. Take after completing antibiotic courses.
Avoid condoms lubricated with nonoxynol-9, as it disrupts vaginal flora. Use plain water-based lubricants instead. Barrier protection with male or female condoms reduces BV recurrence risk.
If you have a regular female sexual partner, simultaneous treatment reduces ping-pong reinfection that drives recurrence. Discuss concurrent treatment with your clinician.
Speak to a Clinician About Bacterial Vaginosis
A licensed clinician at The GP Service can assess your BV symptoms, prescribe appropriate antibiotic treatment, and advise on preventing recurrence — all online, quickly and confidentially.
Expert clinical advice, when you need it.
Bacterial Vaginosis FAQs
BV is caused by an imbalance in vaginal bacteria and is not a sexually transmitted infection, though it is more common in sexually active women. You do not need to treat a male partner. However, BV is more common in women who have female sexual partners, and concurrent treatment of female partners may reduce recurrence. Condom use helps by preventing semen from raising vaginal pH. If you have BV alongside symptoms of STI risk (new partner, unusual discharge type), an STI screen is sensible alongside BV treatment.
Metronidazole (antibiotics) do not cause direct harm to fertility. BV itself, however, particularly in pregnancy, is associated with preterm birth and second-trimester miscarriage. Ascending BV infection can contribute to endometritis and pelvic inflammatory disease, which may affect the fallopian tubes. Treating BV promptly, especially if trying to conceive or pregnant, protects reproductive health. Treatment is safe in the second and third trimesters of pregnancy.
No. BV is not a sexually transmitted infection. You cannot catch BV directly from a sexual partner. However, sexual activity — particularly with new or multiple partners — can alter the vaginal pH and microbiome in ways that predispose to BV. Male partners do not need treatment. Female partners may benefit from simultaneous treatment to prevent recurrence. BV can still occur in women who have never been sexually active.
Boric acid vaginal suppositories (600mg nightly for 14 days) are highly effective for recurrent or antibiotic-resistant BV, with clinical success rates of 70–90%. They work by reducing vaginal pH and directly inhibiting BV-associated organisms. Boric acid is not recommended during pregnancy. It is available from specialist pharmacies and online without prescription, but should be used under clinical guidance. It must only be used vaginally — never taken orally, as it is toxic if swallowed.
Vaginal discharge has a distinctive smell — a mild, slightly acidic scent is entirely normal and reflects the healthy acidic pH of the vagina. A strong fishy smell, particularly after sex, is the hallmark of BV. A yeasty or bread-like smell may suggest thrush. A foul or putrid smell may indicate an STI, foreign body (e.g. forgotten tampon), or pelvic infection. If your discharge smells markedly different from usual, seek clinical assessment.
Yellow discharge is abnormal and should always be investigated. The most common causes are chlamydia, gonorrhoea, or BV. Yellow-green frothy discharge is characteristic of trichomonas. In some cases, yellow discharge may reflect cervicitis or pelvic inflammatory disease. Unlike white discharge (which can be normal or indicate thrush), yellow discharge of any consistency warrants a clinical assessment and STI screen.
Post-coital (after sex) bleeding is not normal and always warrants investigation. Common causes include cervical ectropion (a benign overgrowth of cervical cells onto the outer cervix), cervicitis (cervical inflammation from infection), cervical polyps, or — rarely — cervical cancer. Any woman experiencing regular post-coital bleeding should be seen by a clinician for a speculum examination. Post-coital bleeding alongside unusual discharge should prompt STI screening.
A forgotten or retained tampon causes a foul-smelling, brown or blood-stained vaginal discharge, sometimes with pelvic discomfort. If you suspect a retained tampon or foreign body, do not panic — it can usually be removed by a clinician with a speculum examination. Do not attempt blind digital removal at home as this risks pushing it further. The discharge and smell will resolve rapidly once the foreign body is removed. A short antibiotic course may be prescribed.