Something about your discharge has changed, or there is an itch or an odour you had not noticed before. Both complaints are part of ordinary life for a great many people with a vagina, since bacterial vaginosis affects 23 to 29 per cent of women of reproductive age depending on the region (Peebles et al., Sexually Transmitted Diseases 2019) and 70 to 75 per cent go through at least one episode of thrush in their lifetime (German, Austrian and Swiss gynaecological societies, S2k guideline on vulvovaginal candidosis, 2022). Which of the two is behind it often shows only on a second look.

Telling bacterial vaginosis or thrush apart comes down to a few things you can notice yourself, so it helps to look at what the discharge is like, whether an odour comes with it and which of the two is louder.

Why bacterial vaginosis and thrush get mixed up so often

Both announce themselves through a change in discharge and both can itch or burn, which is where the overlap comes from. How often the guess goes wrong was measured in a study of 95 women buying an over-the-counter antifungal at a pharmacy: 34 per cent of them actually had thrush and in 46 per cent the self-diagnosis delayed the correct one (Ferris et al., Obstetrics & Gynecology 2002). How confident the women felt about their own assessment said nothing about whether they were right.

The specialist literature treats the two as the classic mix-up as well, because people affected by them confuse them routinely. With symptoms that feel new or different, it is worth having a look rather than repeating whatever worked last time.

What bacterial vaginosis does to the vaginal environment

A healthy vagina is dominated by lactobacilli, the lactic acid bacteria that keep the environment acidic, which is an environment other organisms struggle to multiply in. In bacterial vaginosis those protective lactobacilli are displaced and bacteria of the genus Gardnerella take over (S2k guideline on bacterial vaginosis, 2023).

Those bacteria settle across the lining as a tough film, known as a biofilm, which shields them well. That explains why symptoms come back for so many people after a while, since the guideline points to this biofilm as the reason treatment takes hold less well and episodes repeat. Three or more episodes a year counts as a recurring pattern.

As these bacteria break down proteins in the vagina they also produce amines, the breakdown products behind the characteristic odour. At the same time the vagina loses acidity, so the vaginal pH rises above 4.5.

What does bacterial vaginosis discharge look like?

The typical picture is more discharge than usual, evenly thin and greyish with a slightly milky tone, along with the fishy odour that most people notice first. Itching, redness, burning or pain during sex and when passing urine can come along too, although they sit further in the background.

Bacterial vaginosis can equally run its course with no symptoms at all. Since a finding without symptoms does not automatically call for treatment, the guideline advises against screening women who have no complaints, pregnancy included, with planned conception and high-risk pregnancies as the exceptions (S2k guideline on bacterial vaginosis, 2023). Symptoms during pregnancy are a different matter, as bacterial vaginosis is associated with preterm birth, late miscarriage and a higher risk of accompanying infections, which is why pregnant women with symptoms should be treated.

How does thrush feel?

With thrush the itch leads, joined by burning and a raw, sore feeling across the vagina and vulva, plus a lining that looks red, swollen and glossy, sometimes with small fissures in the skin. The discharge is frequently odourless and ranges from thin and whitish to thick with white curd-like clumps. Pain during sex and when passing urine belongs to the picture as well.

Thrush is caused by yeasts of the genus Candida, of which there are several species. Around 90 per cent of cases involve the most common one, Candida albicans, and roughly 8 per cent a rarer species called Candida glabrata (WHO guidelines for the management of symptomatic STIs, 2021). Which species is involved matters once a treatment stops working, because the rarer ones often respond less well to the standard options (Fößleitner, Gynäkologie 2025). At the same time, yeasts can be found in 20 to 30 per cent of non-pregnant women of reproductive age who have no symptoms whatsoever, so a positive finding on its own is not a reason to treat (WHO, 2021).

The differences between bacterial vaginosis and thrush at a glance

• Odour. Fishy with bacterial vaginosis, frequently absent with thrush.
• Itching. The leading symptom in thrush, possible but usually secondary in bacterial vaginosis.
• Discharge. Thin, even and greyish in bacterial vaginosis, whitish to curd-like in thrush.
• Skin and lining. Often clearly red, swollen and sore in thrush, usually less striking in bacterial vaginosis.
• Vaginal pH. Above 4.5 in bacterial vaginosis.
• Treatment. Antibiotic or local antiseptic for bacterial vaginosis, antifungal medicines for thrush.

Those points give you a direction. Settling the question takes a look under the microscope, not least because mixed findings turn up: in the same study, one woman in five had an inflammation with more than one cause behind it (Ferris et al., Obstetrics & Gynecology 2002).

What else can sit behind discharge and itching

The third common cause of changed discharge is trichomoniasis, a sexually transmitted infection with a single-celled parasite, where more than half of the women affected notice discharge and about half of those with symptoms report vulval itching. It is treated with an antibiotic.

Chlamydia and gonorrhoea, by contrast, settle on the cervix and often stay quiet, since at least half of women with gonorrhoea of the cervix have no symptoms and the share is higher still with chlamydia (WHO, 2021). The look of your discharge therefore says very little about what might be happening at the cervix, which makes a test worthwhile if you have had sex without a condom in the past few weeks. Reality Check covers chlamydia, gonorrhoea, syphilis, HIV and hepatitis C as a home test, with the laboratory result available around 24 hours after the samples arrive. Bacterial vaginosis and thrush sit outside that list, as both rely on microscopy on the spot. With acute symptoms the better route leads to a gynaecology appointment, where an examination and treatment happen in one go.

Sometimes there is no infection involved at all, because a contact reaction of the skin to fragrances, detergents or intimate care products and entirely normal discharge both get taken for thrush on a regular basis.

Is bacterial vaginosis a sexually transmitted infection?

Expert opinion splits here. The WHO states plainly that bacterial vaginosis is not a sexually transmitted condition and makes no provision for treating partners (WHO, 2021). The German-language guideline describes something different, namely that the bacteria involved can be detected in male partners and that transmission is therefore documented, while treating a partner is considered worth weighing only in complex cases, given how limited the evidence remains (S2k guideline on bacterial vaginosis, 2023). Those positions have not been reconciled, which makes it a good topic for the consulting room, particularly with episodes that keep coming back.

What nobody disputes is that sexual activity and changing partners raise the risk of bacterial vaginosis, as do smoking, stress, vaginal hygiene practices, courses of antibiotics, intrauterine devices and a low oestrogen level. Thrush works differently, since it does not count as a sexually transmitted infection and partners are treated only if they have symptoms themselves (WHO, 2021). Here the risk climbs above all after broad-spectrum antibiotics, with up to a third of women developing symptomatic thrush afterwards, and also with poorly controlled blood sugar, in pregnancy and on hormonal contraception with a high oestrogen content (Fößleitner, Gynäkologie 2025).

What gets examined at a gynaecology appointment

Most of the work happens inside a single appointment. A sample of secretion is taken from the lower third of the vagina and assessed as a wet mount, meaning untreated under the microscope, where bacterial vaginosis reveals clue cells, that is lining cells with bacteria clinging to them. The vaginal pH and an odour test go with it, and together with the microscopic picture they make up what clinicians call the Amsel criteria.

Where thrush is suspected, the secretion is examined with saline or potassium hydroxide, which shows yeast cells directly in 50 to 80 per cent of symptomatic cases (Fößleitner, Gynäkologie 2025). A fungal culture is added when symptoms keep returning, the finding stays unclear or the treatment fails to work (S2k guideline on vulvovaginal candidosis, 2022).

Anything you have noticed yourself is useful for the appointment, so how long the symptoms have been there, what the discharge looks like, whether an odour comes with it and what you have already tried. Jotting it down over a few days works well for that.

How bacterial vaginosis and thrush are treated

Bacterial vaginosis is treated with an antibiotic, either as a tablet or as something inserted into the vagina, usually across seven days, with local antiseptics as an alternative. In pregnancy an antibiotic is the preferred option and local antiseptics remain available. Lactic acid and probiotics come in alongside that, as current evidence puts them on the helpful side both for the treatment itself and for preventing relapse. With recurring episodes a longer maintenance course can be offered on top.

A first episode of thrush is treated locally, with antifungal pessaries or cream over one to seven days and additional treatment of the vulva from the outside where that area is involved. For heavy symptoms, or when local treatment is not enough, tablets taken by mouth are available, and since those should be avoided in pregnancy, local treatment is preferred there. Four or more episodes a year count as a recurring pattern, which affects roughly 8 per cent of women (S2k guideline on vulvovaginal candidosis, 2022). A maintenance course with a tapering dose over several months is the usual approach then, with relapses after stopping being common.

Because different triggers sit behind the two, each needs its own treatment. For the same reason antifungal medicines are best kept for confirmed findings, so that they stay effective.

What your vaginal environment appreciates day to day

Lactobacilli do their best work when left alone. That means washing the vulva from the outside with lukewarm water and leaving douching out of it, since rinsing unsettles the environment and also distorts the findings if an examination follows soon afterwards (WHO, 2021). Condoms lower the risk of sexually transmitted infections on top of that, and those can produce similar symptoms of their own.

Which brings things back to where they started: both are common, both respond well to treatment and neither says anything about how clean or how healthy anybody is. If symptoms return several times a year or a treatment leaves them unchanged, a gynaecology appointment is the sensible next step, because that is where it becomes clear what is actually going on.