Bacterial vaginosis develops when the balance of bacteria inside the vagina shifts. Normally, beneficial bacteria keep the vaginal environment acidic (around pH 4.0 to 4.5), which suppresses harmful organisms. When those protective bacteria decline, anaerobic bacteria multiply and take over, raising the pH and producing symptoms like a fishy odor, thin gray-white discharge, and irritation. Roughly 23% to 29% of women of reproductive age have BV at any given time, making it one of the most common vaginal conditions worldwide.
What Actually Happens Inside the Vagina
A healthy vagina is dominated by Lactobacillus bacteria, which produce lactic acid and natural antimicrobial compounds. That acidic environment keeps potentially harmful species in check. BV occurs when Lactobacillus populations drop and organisms like Gardnerella, Prevotella, Atopobium, and others begin to flourish. These anaerobic bacteria thrive in a less acidic environment, and as they grow, they push the vaginal pH above 4.5, which further suppresses Lactobacillus and accelerates the imbalance.
This isn’t an infection you “catch” from a single source the way you catch a cold. It’s a disruption of an ecosystem. Several behaviors and biological events can trigger that disruption, sometimes working together.
Sexual Activity Is the Biggest Risk Factor
BV is not classified as a sexually transmitted infection, but it rarely occurs in people who have never had sex. New or multiple sexual partners are one of the strongest risk factors. Sex introduces new bacteria into the vaginal environment, and semen itself is alkaline, which temporarily raises vaginal pH. Not using condoms increases the risk further because there’s direct contact with both a partner’s bacteria and seminal fluid.
The pattern holds for women who have sex with women as well. Shared vaginal bacteria between partners can shift the microbiome composition for both people, which is one reason BV sometimes seems to pass back and forth within a couple even after treatment.
Douching Disrupts the Vaginal Ecosystem
Douching is one of the clearest, most well-studied triggers for BV. The practice physically washes away the protective Lactobacillus bacteria and introduces detergents or chemicals that can damage the mucosal lining. Research using saline and acetic acid douches found measurable changes in vaginal bacteria within 10 minutes, and it took up to 72 hours for the normal flora to return to pre-douching levels. Stronger antiseptic solutions caused even more dramatic, prolonged disruption, giving harmful organisms a window to outgrow the beneficial ones.
Women who douche regularly have roughly a 21% higher risk of developing BV compared to women who don’t douche at all. The vagina is self-cleaning, so the practice provides no hygiene benefit while actively undermining the body’s own defenses.
Lubricants and Hygiene Products
Scented soaps, body washes, and bubble baths that contact the vulva or vagina can introduce chemicals that suppress Lactobacillus growth. But the research on specific products is particularly striking when it comes to personal lubricants. Lab studies have shown that lubricants containing certain antimicrobial preservatives or spermicides significantly inhibit the growth of all four major protective Lactobacillus species. Some of these ingredients killed beneficial bacteria at concentrations hundreds of times lower than what’s present in the product itself.
Even after just four hours of exposure, lubricants reduced the ability of Lactobacillus to colonize vaginal cells by roughly 98%. If you’re prone to BV, choosing a lubricant matters. Look for products free of chlorhexidine, nonoxynol-9, and parabens. Water-based, pH-balanced lubricants with minimal additives are the safest option for vaginal flora.
Your Menstrual Cycle Creates a Vulnerable Window
Menstrual blood is slightly alkaline, so when it’s present in the vagina during your period, it temporarily raises pH and feeds non-Lactobacillus bacteria. Research tracking women across their full cycle found that harmful bacterial species peaked during days one through five of menstruation and declined steadily afterward. Prevotella, one of the key BV-associated organisms, was significantly more common at the start of the cycle than near the end.
Meanwhile, Lactobacillus populations tended to increase as the cycle progressed and estrogen levels rose. This means the days during and just after your period are when the vaginal environment is least stable and most susceptible to a shift toward BV. It’s also why some women notice BV symptoms seem to appear or worsen around menstruation.
You Can’t Get BV From Toilet Seats or Towels
The bacteria involved in BV live in the moist mucous membranes of the vagina. They don’t survive on dry surfaces like toilet seats, towels, or doorknobs. You cannot develop BV from swimming pools, shared clothing, or casual physical contact. The condition requires a change in the bacteria already living inside the vagina, not exposure to bacteria on external surfaces.
How BV Is Diagnosed
A healthcare provider can typically diagnose BV during a standard pelvic exam using a few straightforward checks: looking at the appearance of vaginal discharge (thin, grayish-white, and uniform), testing the vaginal pH (above 4.5 in BV), checking for a fishy smell when a solution is applied to a sample of the discharge, and examining cells under a microscope for “clue cells,” which are vaginal cells coated in a layer of bacteria. Meeting three of these four criteria confirms BV.
Many women with BV have no symptoms at all. If you do notice symptoms, the hallmark is an off-white or gray discharge with a distinctly fishy odor, sometimes accompanied by burning during urination or mild itching.
Why BV Keeps Coming Back
BV is highly treatable with antibiotics, but recurrence is the real challenge. Between 50% and 80% of women experience a return of BV within 6 to 12 months after finishing treatment. The reason lies in the same ecosystem dynamics that caused BV in the first place. Antibiotics kill the overgrown harmful bacteria but don’t necessarily restore healthy Lactobacillus populations. If the beneficial bacteria don’t recolonize quickly enough, the cycle starts over.
Ongoing exposure to the same triggers, whether that’s a sexual partner carrying the associated bacteria, continued douching, or use of irritating products, makes recurrence more likely. Researchers are exploring whether applying Lactobacillus directly to the vagina after antibiotic treatment could help prevent relapse by jumpstarting recolonization, since these bacteria produce the lactic acid needed to keep pH low and suppress harmful organisms long-term.
Reducing Your Risk
Because BV results from an ecological shift rather than a single cause, prevention is about minimizing disruptions to your vaginal bacteria:
- Skip douching entirely. Your vagina maintains itself. Warm water on the external vulva is sufficient for hygiene.
- Use condoms. They reduce the introduction of new bacteria and buffer the alkaline effect of semen.
- Choose products carefully. Avoid scented soaps, sprays, or wipes near the vagina. Select lubricants that are pH-balanced and free of spermicides or harsh preservatives.
- Be aware of your cycle. The days during and just after menstruation are when your vaginal flora is least stable, so minimizing other disruptions during that window can help.
- Wear breathable underwear. Cotton fabrics allow airflow and reduce moisture buildup that favors anaerobic bacteria.