Is BV sexually transmitted? What the research shows

Author: Jessica Lloyd
Senior Vulvovaginal Specialist Naturopath | BHSc(N) | ISSVD, ISSWSH, BSSM, ATMS

Last reviewed: July 4, 2026

For decades, the official line was that bacterial vaginosis (BV) was not sexually transmitted, just a bit of bad luck with your own bacteria. That line is now changing. The newest and best research says that yes, BV can be passed back and forth between sexual partners, and a landmark 2025 trial showed that treating the male partner too cut a woman’s chance of BV coming back almost in half.

So is BV sexually transmitted? The honest answer is: often, but not always.

It behaves like a sexually transmissible condition in a lot of people, while still turning up in women who have never had sex of any kind. Here is what the science actually shows, and what it means if your BV keeps coming back.

Is BV sexually transmitted?

For a long time BV sat in an awkward spot. It was clearly linked to sex – new partners, multiple partners, a female partner and not using condoms all raise your risk – yet it was never officially called a sexually transmitted infection (STI).

Part of the reason is that BV is not one single germ you catch, like chlamydia. It is an overgrowth of bacteria that are already part of the vaginal ecosystem, which made the whole picture muddier.

What has shifted is the weight of evidence. The bacteria that drive BV have been found living on and in penises, and they can be swapped between partners during sex. Women who have never been sexually active are much less likely to get BV.

Female couples show very high rates of BV in both partners. Put it all together and BV looks a lot like something that is, at least partly, sexually transmitted.

The big caveat is that it is not only about sex, which is why researchers tend to say BV is sexually transmissible rather than flatly calling it an STI. More on that below.

What the latest research shows

The study that really moved the needle was published in the New England Journal of Medicine in 2025. Researchers in Australia ran an open-label trial, nicknamed StepUp, with 164 monogamous couples where the woman had symptomatic BV.¹

Half the couples had the woman treated on her own, the usual approach. In the other half, both the woman and her male partner were treated at the same time.

The women were given standard antibiotics. Their male partners took oral metronidazole twice a day for seven days, and also rubbed 2 per cent clindamycin cream onto the penis and upper shaft twice a day for seven days. That combination of an oral and a topical treatment turned out to matter.

Within 12 weeks, BV came back in 35 per cent of the women whose partners were also treated, compared with 63 per cent of the women treated alone.¹ That is close to a halving of the recurrence rate.

The benefit was so clear that the trial was stopped early. The men did report side effects such as nausea, headache and a metallic taste, but nothing serious.

This was not a one-off fluke. An earlier pilot study had already shown that treating male partners with the same oral-plus-topical combination knocked down the BV-associated bacteria living on their genitals.²

What is interesting is that older partner-treatment trials, which mostly used a single oral antibiotic on its own, had failed to help.³ Treating the skin of the penis as well as the gut seems to be the piece that was missing.

A quick word of caution before anyone marches their partner to the pharmacy. In late 2025, a major obstetrics and gynaecology body (ACOG) updated its guidance to say doctors should consider treating the partner in recurrent BV, though not every guideline has caught up yet.⁴ Either way, these are prescription medicines that need a doctor.

So it is a conversation to have with a clinician rather than something to sort out yourself. The direction of travel, though, is unmistakable.

The Gardnerella biofilm, and why it passes between partners

To understand why treating a partner helps, it is worth knowing about the sticky little structure at the heart of stubborn BV. The main organism involved is Gardnerella, which can clump together into a biofilm – a cohesive raft of cells that glues itself to the vaginal wall and acts as a kind of shield.

This is where the older research, still solid today, comes in. Back in 2010, Swidsinski and colleagues looked at urine from more than 350 people, including pregnant women and their partners.⁵

They found Gardnerella in two forms. A cohesive, biofilm-forming type clung to cells in dense clusters, and a loose, dispersed type floated around mixed in with other bacteria.

The cohesive, biofilm form was the telling one. It showed up in everyone with confirmed BV and in their partners – around 7 per cent of men and 13 per cent of women in one group, and 16 per cent of pregnant women alongside 12 per cent of their male partners.

It was not found in healthy lab staff or in children. The dispersed form, by contrast, turned up more randomly and was not linked to sexual partners.

The authors concluded that this cohesive Gardnerella biofilm is a distinct, definable thing that involves both sexes and is passed on sexually. They even suggested it deserved its own name: gardnerellosis.

In plain terms, the biofilm can sit on a penis that has been inside an affected vagina, and be carried back to re-seed the vagina after treatment. That is the re-infection loop that keeps so many couples stuck.

Our understanding of Gardnerella itself has also grown up since then. What was once treated as a single species has been split into several – including Gardnerella vaginalis, Gardnerella leopoldii, Gardnerella piotii and Gardnerella swidsinskii – with research suggesting some types are more aggressive biofilm-builders than others.⁶ It is one reason BV can behave so differently from one person to the next.

But BV is not only about sex

This is the part that gets lost when headlines declare BV an STI, because it is not the whole story. BV also occurs in women who are sexually inexperienced, meaning they have never had any kind of sex with anyone. So sex is clearly not the only route in.

BV is really a state of imbalance. When the protective vaginal bacteria, mostly Lactobacillus species, lose their grip, disruptive bacteria such as Gardnerella move in and the vaginal pH climbs. Plenty of things can tip that balance without a partner involved at all – your hormones, your period, douching and harsh washes, antibiotics, smoking, and even your genes, which help decide how sturdy your protective bacteria are in the first place.

So the most useful way to hold both truths at once is this. In many couples, an untreated partner keeps reintroducing the bacteria, which is why partner treatment helps so much.

In other people, BV flares because of something happening in their own body and environment. For a lot of women with recurrent BV, both things are going on together.

What this means for your vagina

For your vagina, this is encouraging, especially if your BV keeps boomeranging back. If part of the reason it returns is a partner quietly carrying the bacteria, then treating them, on top of treating you, gives your vaginal microbiome a real chance to settle without being knocked over again every few weeks.

It also reframes recurrent BV. If you have been blaming yourself, or feeling like your body is broken because the symptoms keep coming back, the science says otherwise.

Recurrence is usually a re-infection problem and a biofilm problem. It does not mean you did the treatment wrong, or that something is wrong with you.

In our clinic, recurrent BV is one of the most common reasons people come to us, and the women who finally break the cycle tend to be the ones who step back and look at the whole picture – the biofilm, the protective bacteria that need rebuilding, the everyday triggers, and yes, the partner – rather than treating the same flare over and over and hoping it sticks.

Worth knowing too: BV is not just a nuisance. An ongoing imbalance can make the vaginal environment more welcoming to other sexually transmitted infections, and a Lactobacillus-rich vagina is part of what keeps that risk down. Sorting out BV is doing more for you than just clearing the discharge and smell.

Frequently asked questions

Can my partner give me BV?

They can carry and pass on the bacteria involved in BV, yes. The cohesive Gardnerella biofilm has been found on penises, and the 2025 trial showed that treating male partners cut recurrence in women.¹ It is not a clean one-germ infection like chlamydia, but in practice a partner can keep re-seeding your vagina after you have been treated.

Should my male partner be treated for BV?

If your BV keeps coming back, it is now a reasonable thing to raise with a doctor. The trial that showed a benefit used a specific combination of an oral antibiotic plus a cream applied to the penis.¹ In late 2025 ACOG started recommending that doctors consider this for recurrent BV,⁴ though other guidelines are still catching up, and because these are prescription medicines it needs a clinician rather than a guess at the pharmacy.

Can you get BV without having sex?

Yes. BV turns up in women who have never had sex, because it is fundamentally an imbalance in the vaginal bacteria. Hormones, your period, douching, antibiotics, smoking and your own genetics can all tip the balance with no partner involved.

Why does my BV keep coming back after antibiotics?

Two big reasons. First, the Gardnerella biofilm shields the bacteria so antibiotics do not fully clear them, and it can regrow.

Second, if a partner is carrying the bacteria, you can be reinfected soon after finishing treatment. Rebuilding your protective bacteria afterwards matters too.

Does using condoms help?

Consistent condom use is linked to lower rates of BV, which fits with the idea that sex and an untreated partner play a role. It is a simple, low-risk thing to try while you are getting on top of things.

Is BV officially an STI or STD now?

Not officially, not yet. But the evidence that it is sexually transmissible has piled up to the point where some researchers think reclassification is coming. For now, the practical takeaway matters more than the label: if your BV is recurrent, your partner may be part of the picture.

What to do next

If this is your first brush with BV, a single round of treatment and some attention to your protective bacteria is often enough. If you have been round the loop more than once, it is worth getting properly investigated rather than treating blind. A comprehensive vaginal microbiome test can show exactly what is going on in there, which makes treatment far more targeted.

You can work through the whole approach for free in our guide to treating BV naturally, which covers clearing the disruptive bacteria, tackling the biofilm and rebuilding the protective ones. If you want extra help with the biofilm side, a targeted vaginal antimicrobial like BV Rescue is built for exactly that job, and a vaginal probiotic suppository can help repopulate the good bacteria afterwards.

And if your BV simply will not stay gone, that partner conversation is now firmly on the table. We have supported men through BV treatment for over a decade, since the early research showing men can carry and pass it on, and our free Killing BV penis guide walks a partner through exactly what to do. Take the 2025 research to your doctor, and think about getting alongside a practitioner who treats recurrent BV as a whole-picture problem. You can book an appointment with our clinic if you would like a hand untangling it.

This article is general information, not a substitute for personalised medical advice. If your symptoms are persistent, severe or you are pregnant, please see a healthcare provider.