We all know having sex without a condom comes with obvious risks, like STIs and pregnancy. Unprotected sex during one-night stands may also be responsible for a common vaginal infection among women — bacterial vaginosis (BV). Researchers at Melbourne Sexual Health Center in Australia have found women who engage in condomless sex have higher levels of Gardnerella vaginalis and Lactobacillus iners; two strains linked to the poorly understood condition.

“The risk lies in having sex with a new partner, which is a microbial assault on the vagina,” Janneke van de Wijgert at the University of Liverpool, UK told New Scientist.

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Typically in the vagina, there's a balance of "good" bacteria and some "bad" bacteria; good types control the growth of the bad types, according to the Mayo Clinic. However, the presence of BV indicates there's an imbalance, where there's not enough good bacteria to inhibit the expansion of bad bacteria. It frequently develops after having sex with a new partner, but it's not considered an STI.

Among the different five strains of bacteria in the vagina, Lactobacillus species is the most dominant. Women whose vaginas mainly have the L. crispatus strain are considered to be the healthiest, because it promotes a healthy pH, and fights off bacteria, yeast, and other viruses before they form. A study in The Journal of Infectious Diseases found women with L. crispatus had a significantly lower incidence of BV than women with a different vaginal bacteria. However, this balance can be easily disrupted by male ejaculation (semen) and even menstruation, which can lead to the onset of BV-linked bacteria.

This suggests bacteria present on the penis of the new sex partner may cause the vagina to develop an immune response against it, causing inflammation, and potentially BV.

In the new study, published in PLoS One, Lenka Vodstrcil, study author, and her colleagues sought to determine whether various sexual activities could influence the vagina's microbiome, and overall health in a total of 52 volunteers — 19 women did not yet experience penetrative sex at the start. The researchers asked each woman to swab their vaginas every three months for a year, and to write down any type of sex they had. Sexual activities were compared with the types of bacteria identified on each swab.

The findings revealed women who engaged in unprotected penile-vaginal intercourse were more prone to high levels of Gardnerella vaginalis and Lactobacillus iners in their microbiome. Meanwhile, these two strains dominated the vaginal microbiome of first-timers having penile-vaginal sex. Vodstrcil and her colleagues believe similar to other STIs, non-pathogenic bacteria — bacteria that doesn't cause disease — are sexually transmitted.

"Penile-vaginal sex did not alter the consistency of microbial communities but increased G.vaginalis... diversity in young women with and without BV, suggesting sexual transmission of commensal and potentially pathogenic (groups of bacteria)," the researchers concluded.

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However, these findings should be approached with caution; people often lie about sex. It's possible there is a strong link between unprotected sex and imbalanced vaginal bacteria. Regardless, sex without a condom is risky, and can jeopardize the health of a woman and her partner.

The use of probiotic lactobacilli to prevent infection has been under review by researchers. Currently, there are only a few strains that have been clinically proven to be effective, especially in preventing and treating BV. Previous research has found antibiotics with probiotic supplementation can lead to better treatment success rates compared to just antibiotics. Women who took 7-day antibiotics, alongside a probiotic formulation containing the strains Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 for 3 additional weeks, had a success rate of 88 percent compared to 40 percent from the antibiotic group.

The development of probiotics for healthy vaginal microbiome are still under way. Meanwhile, men can help reduce the incidence of BV in their partner by maintaining good penile hygiene. Men who have foreskin should wash underneath; all men should make sure to clean the base of the penis and testicles; and wash the anus where sweat and hair can produce a strong, unpleasant smell.

Wearing a condom during sex can eliminate the spread of bacteria, along with other health conditions.

Source: Vodstrcil LA, Twin J, Garland SM et al. The influence of sexual activity on the vaginal microbiota and Gardnerella vaginalis clade diversity in young women. PLoS One. 2017.

See Also:

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