Bacterial vaginosis (BV) isn’t something you “catch” the way you catch a cold or an STI. It develops when the balance of bacteria already living in the vagina shifts, with protective bacteria declining and other types overgrowing. That said, certain activities, especially sex, clearly trigger this shift, which is why the question feels intuitive. Understanding what actually disrupts that balance is the key to making sense of BV.
What Happens Inside the Vagina During BV
A healthy vagina is dominated by bacteria called Lactobacillus, which produce lactic acid and keep the vaginal pH between 3.5 and 4.5. That acidic environment acts like a built-in defense system, making it difficult for harmful bacteria to thrive.
BV develops when Lactobacillus populations crash and a mix of anaerobic bacteria (types that thrive without oxygen) take over. These include species like Gardnerella vaginalis, Prevotella, Mobiluncus, and others that are normally present in small numbers. When they overgrow, vaginal pH rises into an alkaline range, and the characteristic symptoms appear: thin grayish-white discharge, a fishy odor (often stronger after sex), and sometimes mild irritation. About half of people with BV have no symptoms at all.
Why Sexual Activity Is the Biggest Risk Factor
BV rarely affects people who have never had sex. The CDC notes it occurs most often in those who are sexually active, though researchers still don’t fully understand the mechanism connecting sex to the bacterial shift. Having new or multiple sexual partners is one of the strongest and most consistent risk factors.
Here’s where it gets complicated: BV is not classified as a sexually transmitted infection. Treating a male partner does not reduce a woman’s risk of getting BV or having it come back. However, BV can spread between female sexual partners, which suggests that direct vaginal contact plays a role in transferring the bacteria involved. Not using condoms also increases risk, possibly because semen is alkaline and temporarily raises vaginal pH, giving anaerobic bacteria a window to gain a foothold.
So while you can’t “catch” BV the way you catch chlamydia, sexual activity is clearly a major trigger for the bacterial disruption that causes it.
Douching and Vaginal Products
Douching is associated with a 20% higher incidence of BV. The practice washes away Lactobacillus and disrupts the vagina’s self-cleaning system, creating conditions where anaerobic bacteria can flourish. Interestingly, one small study found that stopping douching for four weeks didn’t immediately decrease BV risk, suggesting the damage to the microbial balance may take time to reverse, or that other factors are also at play.
The vagina cleans itself through natural discharge. Washing the external vulva with warm water is all that’s needed. Scented soaps, sprays, and internal washes can all push vaginal pH in the wrong direction.
Smoking Changes Vaginal Bacteria
Smoking is a less obvious but well-documented risk factor. Nicotine disrupts the vaginal microbiome in several ways: it weakens the immune response in vaginal tissue, reduces the competitive ability of protective Lactobacillus bacteria, and increases the permeability of the vaginal lining. That damaged lining triggers an inflammatory process that makes it easier for harmful bacteria to attach to vaginal cells. Nicotine also interferes with the production of sex hormones, which play a role in maintaining the environment Lactobacillus needs to thrive.
Components of tobacco smoke can even help certain bacteria form protective biofilms, making them harder for the body’s immune system to clear. For people who experience recurrent BV, quitting smoking is one modifiable factor worth considering.
Other Factors That Shift the Balance
Antibiotics taken for other infections (a UTI, a sinus infection) can collaterally wipe out vaginal Lactobacillus, since these drugs don’t distinguish between helpful and harmful bacteria. Hormonal changes during the menstrual cycle, pregnancy, or menopause also affect vaginal acidity and bacterial composition. Stress and a weakened immune system can play a role as well, though these are harder to measure and control.
In many cases, BV develops without a single clear trigger. Multiple small disruptions can stack up over time, eventually tipping the balance.
Why BV Keeps Coming Back
Recurrence is one of the most frustrating aspects of BV. Even after successful antibiotic treatment, many people experience repeat episodes. The anaerobic bacteria involved in BV can form biofilms on the vaginal wall, essentially building a protective shield that antibiotics can penetrate during treatment but can’t fully eradicate. Once treatment ends, the remaining bacteria can re-establish themselves.
Several approaches that sound promising haven’t held up in research. Probiotic supplements and vaginal Lactobacillus formulations have been studied extensively, but no strong evidence supports them as effective treatments or preventive tools. High-dose vitamin D supplementation has also been tested and does not reduce recurrence rates.
What does help: using condoms consistently, avoiding douching, and limiting the number of new sexual partners. For people with multiple recurrences, long-term suppressive therapy with a vaginal antibiotic gel used twice weekly for three months or more can reduce repeat episodes, though the benefit tends to fade once the regimen stops.
Why It Matters Beyond Discomfort
BV isn’t just an annoyance. Having BV increases your chances of acquiring other sexually transmitted infections, including HIV, chlamydia, and gonorrhea. The disrupted vaginal environment and higher pH make it easier for these pathogens to take hold. During pregnancy, BV is associated with preterm birth and low birth weight. These risks make it worth addressing even mild or asymptomatic cases, particularly if you’re pregnant or trying to conceive.