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This Common Infection That Affects Millions Of Women Is Actually An STI

For decades, bacterial vaginosis (BV) has been treated as a frustrating but routine infection—one that afflicts nearly a third of women in the U.S. And often comes back again and again for more than half of patients. But what if the reason for these relentless recurrences isn't just a quirk of the vaginal microbiome?

A groundbreaking new study suggests BV isn't just an imbalance—it's sexually transmitted. And the key to stopping it may not lie in treating women alone but in treating their male partners as well.

"One dominant risk factor… in our clinical studies was a regular partner," says Catriona Bradshaw, an author of the study and a clinician at Melbourne Sexual Health Centre at Monash University. "[It] kept popping out and just smacking us between the eyes, and we got to a point where we thought 'we just have to do a partner treatment trial.'"

Is bacterial vaginosis sexually transmitted?

BV occurs when the perfect storm of bacteria combines in the vagina. Unlike typical sexually transmitted infections (STIs), no single pathogen is responsible. But, it has long been suspected that these bacteria can be sexually transmitted.

"We've had evidence for many years that bacterial vaginosis might be a sexually transmitted infection, based on data that includes increased risk of bacterial vaginosis with increasing number of sexual partners, increased risk with sex without a condom, and other evidence," says David Fredricks, a clinician and microbiologist at the University of Washington. "Although this hypothesis has been out there for many decades, some limited studies of male partner treatment to eradicate BV associated bacteria have not met with success."

(STDs are at a shocking high. How do we reverse the trend?)

In fact, BV has long been treated as an STI in same-sex female partners. "There's been studies since the 80s, and lesbian monogamous couples had astonishingly high concordance for BV," Bradshaw says. "We're talking at 80 percent."

A study she worked on found that lesbian couples had nearly a 20 percent higher rate of BV than the general population of Australia. And, when monogamous same-sex couples entered the study without BV, they also ended it that way, she says. "It's clearly being transmitted between women. So why on earth wouldn't it be transmitted between men and women?" she says.

A scanning electron micrograph shows Lactobacillus bacteria, the beneficial microbes that help maintain a healthy vaginal environment. By producing lactic acid, they create an acidic barrier that wards off harmful bacteria.

Micrograph by Science Photo Library

When anaerobic bacteria like Gardnerella (pictured) outnumber protective Lactobacillus species, bacterial vaginosis can develop. New research suggests BV is sexually transmitted—and that treating male partners may be key to preventing its stubborn recurrence.

Micrograph by BSIP/UIG/Getty Images

A new approach to treatment

To test that idea, Bradshaw and epidemiologist Lenka Vodstrcil studied opposite-sex monogamous couples in which the woman had BV. Unlike past studies, which had failed to show a clear benefit, their research introduced a key difference: In addition to taking oral antibiotics, men also applied a topical antibiotic, clindamycin, directly to the penis.

Bacterial Vaginosis: A New Understanding Of Transmission

Have you ever felt embarrassed or worried after noticing a fishy smell in your genital area? If you're a woman, that smell usually indicates bacterial vaginosis (BV) and can be treated with antibiotics. A new study suggests that BV is not just a concern for women. It turns out that it's a sexually transmitted infection (STI) and a woman's male sexual partners should be treated with antibiotics as well.

Overgrowth of "bad" bacteria.

BV is the single most common diagnosis among women who visit a doctor because of excess fluids (or "discharge") from the vagina. Those fluids often have the odor of "fish." BV is not caused by a single type of bacteria, but, rather, by a shift in the balance between "good" and "bad" bacteria in the vagina.

Bacteria clinging to vaginal cells in bacterial vaginosis

Source: CDC/ M. Rein

The vagina normally has enough "good" bacteria (Lactobacillus) that keeps the internal environment acidic. In BV, the balance is thrown off with harmful bacteria (like Gardnerella vaginalis) growing in abundance.

These bacteria break down proteins and release amines, the same smelly chemicals responsible for fish odor and certain body smells. As the "bad" bacteria grow more, the environment in the vagina becomes less acidic, which makes the smell of these amines more noticeable, especially after sex or during menstruation.

Is BV Dangerous for My Health?

In addition to being an unwelcome visitor, BV also has habit of coming back again: even after treatment, as many as 60% of women have a recurrence within one year after their last infection.

BV has also been associated with increased risk of HIV, bacterial STIs, and spontaneous abortion and preterm delivery in pregnancy.

Thankfully, treatment for BV is straight-forward: take antibiotics that kill the "bad" bacteria and reset the balance in favor of the good bacteria. The standard treatment approach is to take a pill (metronidazole) or to insert an antibiotic cream directly into the vagina for 5-7 days.

How Did the Study Prove that BV is an STI?

Researchers have believed for many years that BV might be sexually transmitted from men to women. But the proof researchers were looking for was missing. Previous studies did not show that treating men for BV stops women from getting BV.

But researchers in Australia just tried a different approach. In addition to giving men pills to treat the bacteria, they also had them apply a cream to the head of their penis. And this produced a blockbuster result.

The study enrolled 164 adult couples who attested to being monogamous.

If a woman was diagnosed with BV, her male partner was randomly assigned to either receive no treatment (placebo) or a combination of oral metronidazole and a 2% clindamycin cream applied to the penile skin.

The trial was so successful that the ethics committee decided to stop it early. When comparing 81 couples in which the male partner was treated to 83 couples in which the male partner was not treated, the risk of the woman having BV come back again was 63% less.

What Does the New Study Mean for You?

This study confirmed that male partners can transmit bacteria that cause BV to their female partners.

If you're a woman with vaginal discharge, a fishy smell, and sexual partners who have a penis, make sure those partners get treated with oral antibiotics and a topical cream.

This finding shifts how we think about BV, categorizing it as a sexually transmitted infection. But with this new classification comes both benefits and challenges.

Is There a Problem Labeling BV an STI?

Words shape how we think about diseases. When doctors label an infection "sexually transmitted," it often triggers moral judgment, fear, and stigma in a way that infections acquired through other routine, healthy activities—breathing, eating, exercising—do not.

People with STIs are often unfairly perceived as 'dirty' or 'reckless,' while those with the flu or a stomach infection face no such stigma.

How will public perception of BV change now that it's an STI? History suggests that the shift could be significant.

Consider cervical cancer: Before it was widely known that human papillomavirus (HPV) caused it, cervical cancer was primarily viewed as a random tragedy. Getting it meant you had bad luck. When the HPV vaccine became a standard public health recommendation, people became widely aware that cervical cancer was sexually acquired. The disease itself remained the same, but our understanding of its transmission changed, reshaping public perception.

A similar debate emerged with Mpox (formerly known as monkeypox). During the 2022 outbreak, the overwhelming majority of cases occurred in men who have sex with men, leading to tense discussions about whether to classify Mpox as an STI. Some public health officials hesitated, worried that the label would fuel discrimination and deter broader awareness of the virus. I and others argued that classifying it as an STI was both scientifically accurate and necessary to target interventions effectively.

These debates highlight a central tension in public health: Labeling an infection an STI can focus attention on effective prevention and treatment, but it also invites stigma that can drive people away from seeking care.

The reality is that sex, like eating or breathing or exercising, is a normal health-enhancing activity for humans, and public health officials should be focused on making all activities as free from infection as possible – without shaming the activity itself. No one hesitates to seek treatment for a gastrointestinal infection after dining at a restaurant or a respiratory illness after flying on a plane. Yet, when an infection is linked to sex, shame and silence too often replace open discussion and medical care.

What Should You Do about BV?

If you are in a sexual relationship and one of you has BV, make sure both partners get treated. Keep in mind that not all doctors are up to date on the latest advances, so point them to this article or the original study.

For our society, I hope that this important medical and scientific advance will make us all healthier and not fuel stigma. Classifying BV as an STI presents an opportunity to improve the health of all of us by expanding treatment to men and women and, over time, reducing the adverse health risks associated with BV in women.

Is Your Irritated Vagina A Yeast Infection Or Bacterial Vaginosis? Here's How To Tell

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So it feels like your vagina is on fire. Let me first say, I'm so sorry you're here. You might initially assume you're dealing with a yeast infection—it's just the vagina problem with the best PR. And as many as 75% of people with vaginas will get a yeast infection over the course of their lifetime, making it a pretty good guess. But there's another condition that can chart a similar course and is actually a more common cause of a painful vagina: bacterial vaginosis, or BV. In as many as half of cases of vaginal discomfort diagnosed by docs, BV is the culprit, according to research. And figuring out whether you're dealing with a yeast infection or bacterial vaginosis is key to getting swift relief from the special hell of a burning, itching crotch.

Both a yeast infection and BV are the result of an overgrowth of certain microbes in your nether regions. But where a yeast infection involves excess of a fungus called Candida (almost always Candida albicans, but sometimes other types like Candida glabrata or Candida tropicalis), bacterial vaginosis occurs with an overload of anaerobic (or non-oxygen-requiring) bacteria, commonly Gardnerella vaginalis. To be clear, every vagina has some amount of yeast and anaerobic bacteria living in there on a good day; you'll only wind up with a problem when the numbers of either surpass their usual quantity, resulting in an imbalance.

Read on to learn how to tell what's throwing things off-kilter down there, how to find relief, and why you might be stuck playing this unfortunate guessing game on repeat.

Here's how yeast infection and bacterial vaginosis symptoms differ.

Both yeast infections and BV can make your nether regions feel supremely uncomfy. But there are some key differences in how they tend to show up, particularly when it comes to vaginal discharge and odor. While yeast brings a thick, white, and clumpy discharge, the BV version is generally thinner and grayer, Carolyn Ross, MD, a board-certified ob-gyn in Burlington, New Jersey, and medical advisor at Winx Health, tells SELF. And with BV, things will probably smell fishy down there, whereas with a yeast infection, there's typically no real smell, she adds.

Also helpful to note: The symptoms of a yeast infection tend to colonize your whole vulva (meaning, your external labia), causing irritation and itching throughout, whereas bacterial vaginosis is concentrated in the vagina, Dr. Ross says, so any discomfort is mostly therein.

To recap, with a yeast infection, your symptoms will likely include:

Itching, irritation, and pain in your vagina and vulva

Swelling and discoloration of your vulva

Burning in your vagina when you pee or have sex

Cottage-cheese-like discharge with little or no smell

And with bacterial vaginosis, your symptoms will generally include:

Pain or irritation in your vagina

Burning in your vagina when you pee or have sex

Light gray (or off-white or greenish) discharge with a fishy smell, which may be especially noticeable after sex

Keep in mind, too, that these similarly presenting conditions also have some symptom overlap with common STIs, Dr. Ross says, like trichomoniasis, gonorrhea, and chlamydia, so it's important to see your doctor if you're not quite sure whether yeast or BV fits the bill (more on this below). Another disconcerting possibility is that you're rockin' a case of both yeast and BV at the same time. It's not common, but it can happen if your vaginal flora (a.K.A. The community of microbes living there) "gets really out of whack," Kenosha D. Gleaton, MD, a board-certified ob-gyn in Charleston and medical advisor for Everlywell, tells SELF. "And double the trouble just means double the discomfort."

Relatedly, if you have BV and then take antibiotics to treat it, you might be at higher risk of developing a yeast infection afterward, Dr. Ross says. That's because the meds might not just kill off the harmful bacteria; they could also knock out some of the good guys that are typically responsible for keeping yeast in check.

Certain factors can make you more prone to yeast, BV, or both.

Adding to the potential yeast-BV confusion is the fact that they share many of the same risk factors. That's because anything that can mess with the delicate harmony of your vaginal flora—and lower your numbers of "good" bacteria like Lactobacillus—can also open the door for an overgrowth of either "bad" bacteria like Gardnerella (bacterial vaginosis) or Candida (yeast). So you want to avoid any douching or washing inside your vagina (just stick to your vulva), and steer clear of scented soaps, detergents, or menstrual products—since all of the above can throw off that balance. Similarly, taking antibiotics for a sickness or skin infection elsewhere in your body could up your risk of yeast or BV by wiping out some of those good vaginal microbes.

While neither BV nor yeast is sexually transmitted, changes in your sex life—having sex with a new person or switching between multiple partners—may also raise your risk of either, Dr. Ross says. After all, you're exposing your vagina to a different set of microbes (the ones populating your new partner's genitals), which could mess with your ecosystem. Similarly, having your period won't cause either condition, but the hormonal changes and presence of blood down there could switch up your typical vaginal microbiome and make you more susceptible to both. Same goes for having an intrauterine device (IUD); research suggests that copper ones, specifically, might restrict the growth of good bacteria relative to bad guys, predisposing you to BV, while portions of any IUD could also act as spaces for yeast to multiply.

That said, there are also a few unique factors that could up your likelihood of a yeast infection or bacterial vaginosis. On the yeast front, candida "loves warm, moist environments," Dr. Gleaton says, so wearing tight or damp clothing (like a wet bathing suit or sweaty workout clothes) for a long period of time might leave you abnormally yeasty. These microbes also go ham for sugar, so if you have an elevated blood-sugar level (as with diabetes) or use flavored or warming lubes containing a type of sugar called glycerin, you could be at higher risk. For the same reason, having extra-high estrogen levels—like during pregnancy or while taking estrogen therapy—could set off yeast overgrowth, as estrogen raises the level of glycogen (a stored form of glucose) in your vagina. As for BV-specific risk factors? There's evidence to suggest smoking could directly reduce your levels of helpful Lactobacillus bacteria, allowing for the BV-causing bugs to overpopulate.

A correct diagnosis is important, because treatment for a yeast infection vs. Bacterial vaginosis looks pretty different.

Because yeast infections and BV involve overgrowth of two distinct organisms, curbing that excess requires two different types of medication: an antifungal for yeast and an antibiotic for BV.

In the case of yeast, there are a bunch of popular OTC antifungal creams and suppositories (which dissolve inside your vagina), including miconazole (Monistat) and tioconazole. If you feel confident that you're dealing with yeast (perhaps you've gotten this type of infection before), it's generally okay to treat your symptoms on your own with one of these solutions over the course of three to seven days. Just note that if you're still dealing with pain and discharge past that period, it may be a sign that you've taken the wrong medication; if, for instance, it's actually BV and you're using OTC yeast infection treatments, you won't get any relief…and you could even make things more uncomfortable down there.

That's why it's generally a good idea to give your doctor a call if you're at all unsure of what's plaguing you. An ob-gyn can often pinpoint a yeast infection based on symptoms alone, but they can also gently swab your vagina and use a microscope to check your discharge for signs of yeast or bacterial overgrowth. And if they suspect that something else might be in play, they can send that swab out for a culture test too. This typically checks for a bunch of heavy hitters at once, Dr. Ross says, including, yes, BV and yeast, but also trichomoniasis, chlamydia, and gonorrhea. (If you can't get in to see your doc for whatever reason, there are also at-home culture and vaginal pH tests available that can give you insight into what's going on and, in some cases, connect you to a telehealth provider to interpret the results and prescribe you meds if needed.)

If a yeast infection is the culprit, your doc can prescribe an antifungal called fluconazole (Diflucan), which is a one-time pill that can knock out candida overgrowth. (Dr. Ross favors it over the OTC creams, given that ingredients in the latter can sometimes trigger allergic reactions.) And as for BV? The only treatments are prescription antibiotics—typically metronidazole (Flagyl). It comes in the form of a pill, which you'd take twice a day for a week, or you can get it as a vaginal gel that you insert every night for five nights, Dr. Ross says. Other common options include clindamycin (Cleocin, Clindesse), which comes as a pill, cream, or suppository, and Tinidazole (Tindamax), which is taken as a pill.

It's especially important to see a doc if you're dealing with recurrent infections—whether yeast or BV.

Getting either one of these infections at some point is basically a fact of life for people with a vagina and is generally NBD, given that the above antifungals and antibiotics can usually knock them out. But in some cases, your vagina might struggle to find a happy state of balance post-infection, leading to repeat appearances of BV or yeast—both of which will require a personalized treatment plan created by your doctor to resolve.

Aside from the factors above that could put you at risk for BV or yeast, it's also possible that the natural composition of your vaginal flora just makes you more susceptible, Dr. Ross says. Or if you're immunocompromised in any way or on consistent antibiotics for a different condition, your body could have a harder time fighting off either infection. In the case of yeast, you could also be dealing with an atypical fungus like Candida tropicalis or Candida glabrata, which may require a specific type of antifungal. Or for whatever reason, your particular brand of BV or yeast may just need a stronger or longer dose of meds to eradicate.

Unsurprisingly, the treatment for recurrent BV or recurrent yeast tends to involve extending the usual care—that is, doing a lengthier course of antibiotics for BV or antifungals for yeast as determined by your doctor, for up to six months. In certain scenarios, your doc might suggest trying boric acid suppositories, which may help acidify things down there in a way that hinders the growth of either microbe. (But this is generally a last-ditch effort, given boric acid's efficacy isn't super well supported.) And they can also help determine whether an underlying condition might be messing with your immune system, hormones, or blood sugar levels in a way that's opening you up to yeast infections or BV on the reg.

Brushing up on some basic vaginal hygiene could also help mitigate repeat yeast or BV (even if both often happen for reasons beyond our control). As Dr. Ross notes, it can't hurt to use a sensitive skin-friendly laundry detergent, opt for scent-free soap and menstrual products, wear loose cotton underwear, and make a point to change out of a wet bathing suit or sweaty gym clothes as soon as possible. It might be a little extra maintenance, but it can go a long way toward keeping your vagina cool and calm—so you can be too.

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