Can Bacterial Vaginosis Be Transmitted Sexually? Research Says Yes

Key Points

• Bacterial vaginosis, or BV, is sexually associated but not a sexually transmitted infection (STI).
• Male partners can pass BV to female partners.
• Women with symptoms of BV may want to have their male partners treated to avoid reinfection.

Bacterial vaginosis (BV) occurs due to a bacterial imbalance in the vagina but is rarely associated with sexual transmission of that bacteria to men. Although men can't get BV, it's suspected that men could be carriers and transmitters of the bacteria.

Bacterial vaginosis is not a sexually transmitted infection (STI), but may be sexually associated. And now, science offers more revealing data.

What causes bacterial vaginosis?

Bacterial vaginosis is a common vaginal infection in which the "bad" bacteria outnumber the "good" bacteria. When the natural balance of bacteria is thrown off, it increases the chance of infection.

"Anything that can shift the delicate balance between the good and bad bacteria can increase the risk of BV," said Allison K. Rodgers, M.D., a board-certified OB-GYN specializing in reproductive endocrinology and infertility with Fertility Centers of Illinois in Glenview and Buffalo Grove.

"Bacterial vaginosis is the decline of the normal lactobacilli, which are the healthy bacteria in the female reproductive tract, and an overgrowth of specific pathologic bacteria that can cause abnormal discharge, smell and infection in the vagina," Rodgers said.

Not everyone experiences symptoms of bacterial vaginosis, which includes a fishy-smelling vaginal discharge or itching. About 84 percent of women with BV lacked the symptoms of BV, the Centers for Disease Control and Prevention (CDC) shared.

Roughly 35 percent of women or people with a vagina will experience BV, according to Cleveland Clinic. The risk of getting BV may increase in sexually active women with multiple sex partners who don't use a condom. This is due to changes to the bacteria in their vaginas.

Bacterial vaginosis is often treated with a course of antibiotics, although it may reoccur. Researchers have discovered that the male partner may reintroduce a BV infection to female partners.

How does sex affect the microbiome?

Researchers at the Indiana University School of Medicine analyzed the urethral microbiome in healthy men without sexually transmitted diseases (STDs). They surprisingly found bacteria associated with bacterial vaginosis during the 2023 study.

"This is an interesting paper. Why? Because for many years, we have basically said that BV is not a transmissible infection—unlike gonorrhea, chlamydia, etc. But with results like this, it does imply that it is transmissible," said Mary Jane Minkin, M.D., an OB-GYN and clinical professor at the Yale School of Medicine, in New Haven, Connecticut.

"These bacteria can be transmitted through heterosexual, vaginal sex, something that has never been shown in research before," said David E, Nelson, Ph.D., a professor of microbiology and immunology at the Indiana University School of Medicine in Indianapolis and corresponding author of the study in a press release.

Recommended

• What You Should Know about Bacterial Vaginosis: If uneven vaginal pH leads to bacterial vaginosis, you should know how to respond.
• Bacterial Vaginosis vs. Yeast Infection—What's the Difference?: Understanding the differences between these conditions can help you determine the best treatment.
• What's the Link Between Bacterial Vaginosis and Menopause?: Hormonal changes are the main reason BV is prevalent in menopausal women.

Most previous human microbiome studies ignored sexual behavior, the researchers said. However, it's possible the human microbiome may be behaviorally determined.

These findings may change the way infections such as vaginosis are treated and how patients are educated about sexual health and care.

"They haven't worked out all the details in this paper, and they note that, but to me, the major take home message is that if a woman is treated for BV and ends up with a recurrence that many women do, it may well be appropriate to treat her male partner as well, as she may be being reinfected," Minkin said.

Can men get bacterial vaginosis?

Although men won't feel the effects of bacterial vaginosis, they can transmit the bacteria to their female partner.

Men who reported having vaginal intercourse also carried the bacteria. Researchers examined 110 urethral swab samples from men with no sexually transmitted infections, no urogenital symptoms and no inflammation of the urethra.

These men had colonized bacteria native to the penile urethra and another from an external source. The research team detected the bacteria associated with vaginosis for at least two months after vaginal intercourse.

"Our research provides the first healthy baseline for clinicians and scientists to compare with diseased urogenital states," said Evelyn Toh, Ph.D., an assistant research professor of microbiology and immunology at the Indiana University School of Medicine and the study's lead author, in a press release. "We may be able to offer new insights into bacteria's role in urogenital diseases."

Can safer sex help prevent a BV recurrence in women?

Women can better protect themselves against bacterial vaginosis. Safer sex could help reduce a woman's risk of BV reinfection. Use condoms during sexual intercourse and clean your sex toys after each use.

"If one does have casual sex, you must use a condom as well as your contraceptive methods such as the pill or IUD to prevent not only STIs but also BV," Minkin said.

"There is still a stigma in talking about sex, and hence STIs are often overlooked," Toh said. "However, STIs really impact women and minorities disproportionately, as well as socioeconomically disadvantaged people."

Why should you take care of bacterial vaginosis?

Bacterial vaginosis can often resolve without treatment. The body can restore balance; about one-third of people with a vagina have BV without issues, Rodgers said.

Treatment is necessary during pregnancy, she added, as well if you're bothered by discharge or smell or when you're having a medical procedure that could push the infection higher into the uterus.

"It makes regularly known STIs such as gonorrhea or chlamydia more transmissible," Minkin said. "Also, if a woman does have BV and gets pregnant, she runs a higher risk of going into preterm labor when she gets pregnant. So, all of this is relevant."

"BV does raise the pH of the vagina, but this does not cause issues with fertility. It can, however, lead to pregnancy complications, such as preterm delivery. So we do treat BV in pregnancy," Rodgers said.

What do studies have to say about BV and uncircumcised penises?

Uncircumcised men with more than one female sexual partner were more likely to carry bacteria associated with bacterial vaginosis on their penis, according to a 2015 study published by the American Society for Microbiology.

"Our findings suggest that the uncircumcised penis is an important niche for BV-associated genital anaerobes," stated the study's authors. "Reducing bacterial exchange by barrier methods and managing carriage of BV-associated bacteria in men may decrease BV persistence and recurrence in women."

Is BV recurrence caused by untreated partners?

High rates of BV recurrence may be due to treatments targeting women only, meaning male partners potentially may be reinfecting women, suggested an Australian study in progress (2019-2023).

The trial, which they are conducting in more than 300 couples, focuses on preventing recurrence with simultaneous treatments using oral and topical antibiotics. If proven effective, the researchers will propose new treatment strategies.

The couples are monitored for three months and divided into two groups—with men receiving treatment and another group without treatment. The study attempts to test the hypothesis that women who do not use condoms or who have the same sexual partner before and after treatment are more likely to have a recurrence.

Until now, treatment is effective in the short term, but 1 in 2 women experience recurrence within six months of treatment for BV, according to the researchers. So, timely treatment in both men and women could potentially help lower reinfection rates in women.