Bacterial vaginosis can contribute to an abnormal Pap smear result, though the relationship is more layered than a simple yes. BV triggers inflammation and cell changes in the cervix that a lab may flag as atypical, and a large cross-sectional survey of over 9,000 women in China found that BV roughly doubled the odds of abnormal cervical cytology even after accounting for high-risk HPV status. But the picture gets more complicated when you separate what BV does directly to cervical cells from what it does indirectly by helping HPV gain a foothold and stick around.
How BV Appears on a Pap Smear
A Pap smear collects cells from the surface of the cervix and examines them under a microscope. The lab is mainly looking for precancerous or cancerous changes, but the sample also reveals a lot about the vaginal environment. When BV is present, the slide typically shows what are called “clue cells,” which are normal epithelial cells covered with a coating of bacteria. One study examining Pap smears at a tertiary health center found BV in about 17% of all smears, making it the most common cervicovaginal infection detected during screening.1Nepal Medical College Journal. Study of Trichomonas Vaginalis and Bacterial Vaginosis in Pap smear at a Tertiary Health Care Centre of Nepal Another study found that among smears showing signs of infection, about three-quarters contained clue cells and a notable absence of lactobacilli, both hallmarks of BV.2Wiley Online Library / Diagnostic Cytopathology. Clinicopathological study of Papanicolaou (Pap) smears for diagnosing of cervical infections
These findings on a Pap smear don’t automatically mean you have precancerous cells. The lab report might come back noting “reactive changes associated with inflammation” or “shift in vaginal flora consistent with bacterial vaginosis.” These are descriptive comments, not diagnoses of dysplasia. However, the inflammatory backdrop that BV creates can muddy the picture enough that the lab flags the sample as abnormal or unsatisfactory, prompting follow-up.
When Inflammation Mimics Precancerous Changes
This is where things get tricky for both the lab and the patient. The chronic irritation from BV can cause the cervical cells to undergo changes like parakeratosis, hyperkeratosis, and squamous metaplasia. These are the cervix’s way of protecting itself from ongoing irritation, but under a microscope, they can look uncomfortably similar to the cell changes caused by HPV.3PubMed Central. The Pap smear in inflammation and repair A cytotechnologist reading the slide has to decide whether the atypical-looking cells are reactive (the cervix responding to inflammation) or truly precancerous, and that distinction is not always clear-cut.
The result is that some BV-related Pap abnormalities land in the “atypical squamous cells of undetermined significance” category, commonly known as ASC-US. This is the mildest abnormal finding and essentially means the cells look unusual but the lab can’t say whether the cause is something harmless or something that needs watching. One study looking specifically at patients with ASC-US Pap results found that 41% of them had BV.4Obstetrics & Gynecology. The association between abnormal cervical cytology and bacterial vaginosis That’s a high proportion, and it raises the question of how many ASC-US results are driven by BV-related inflammation rather than genuine precancerous activity.
The practical impact for you: if you receive an ASC-US result and you know you have BV or symptoms consistent with it, treating the BV and repeating the Pap can clarify whether the abnormality was inflammation-driven. Many providers will follow exactly this approach before escalating to more invasive workups.
Does BV Directly Cause Precancerous Changes, or Just Look Like Them?
The evidence here splits in an interesting way. Some research suggests that BV is independently linked to abnormal cervical cytology. The large Chinese survey mentioned earlier, which included over 9,000 community-dwelling women, found that BV was associated with roughly twice the odds of abnormal cervical cytology even after adjusting for whether the woman was positive for cancer-causing strains of HPV.5PLOS ONE. Associations of sexually transmitted infections and bacterial vaginosis with abnormal cervical cytology: A cross-sectional survey with 9090 community women in China
But other research paints a different picture. A European study comparing women with major Pap smear abnormalities (high-grade lesions) to those with normal or minor findings found that BV rates did not differ significantly between the two groups. That study concluded that BV on its own was not independently associated with an increased risk of major cytological abnormalities.6PubMed. Bacterial vaginosis, aerobic vaginitis, vaginal inflammation and major Pap smear abnormalities In other words, BV might nudge a Pap into the mildly abnormal range through inflammation, but it may not be the sole driver pushing cells toward serious precancerous change. The heavier lifting on that front appears to involve HPV.
This disagreement in the literature matters because it shapes how clinicians respond to your results. An abnormal Pap in the presence of BV doesn’t automatically mean you’re on a path toward cervical cancer. But it does mean the cervix is dealing with a disrupted environment that warrants attention.
The BV and HPV Connection
Where BV’s influence on Pap results becomes most concerning is in its relationship with human papillomavirus. HPV, particularly high-risk strains, is the primary driver of cervical cancer. BV doesn’t cause HPV infection, but substantial evidence suggests it makes HPV harder to clear and more likely to cause damage once it’s there.
A systematic review and meta-analysis examining BV and cervical precancerous lesions concluded that BV promotes both the acquisition and persistence of HPV infection.7PubMed Central. Association between Bacterial Vaginosis and Cervical Intraepithelial Neoplasia: Systematic Review and Meta-Analysis A cohort study among Kenyan women found that higher concentrations of Atopobium vaginae, a bacterium strongly associated with BV, were linked to about a 48% increase in the odds of persistent high-risk HPV detection at follow-up. Conversely, higher levels of Lactobacillus crispatus, the “healthy” dominant bacterium in a balanced vaginal environment, were associated with a 50% reduction in the odds of persistent HPV.8PubMed Central. Vaginal bacteria and risk of incident and persistent infection with high risk sub-types of human papillomavirus: a cohort study among Kenyan women
A longitudinal study tracking women who were positive for high-risk HPV drove this point home with striking numbers. Among women with BV at the time of their HPV diagnosis, only about 29% cleared the virus over the follow-up period, compared to roughly 52% of women without BV. Meanwhile, about 24% of women in the BV group showed cytological progression on their Pap smears, compared to only about 10% of the BV-free group. The odds ratio for progression among BV-positive women was substantial, particularly in the larger study cohort.9PubMed Central. Bacterial vaginosis in microscopic examination of Pap smears in patients with high-risk HPV is associated with viral persistence and cytological progression in a longitudinal study
So while BV alone may or may not produce true dysplasia, the combination of BV and HPV is more dangerous than HPV alone. If you have both, the risk of your Pap results worsening over time is significantly higher.
What BV Bacteria Actually Do to the Cervix
The biological mechanisms behind BV’s effects on the cervix help explain why it disrupts Pap results. In a healthy vaginal environment, Lactobacillus bacteria dominate and produce lactic acid, keeping the pH low and creating an inhospitable environment for many pathogens. BV flips this balance. The lactobacilli decline and are replaced by a diverse mix of anaerobic bacteria, particularly Gardnerella vaginalis and Atopobium vaginae. These organisms produce enzymes and metabolites that actively damage cervical tissue.
Research using 3D models of human cervical tissue found that Gardnerella vaginalis significantly reduced levels of MUC1, a protective mucin protein that acts as a barrier on cervical cells. The same bacterium also triggered production of MMP-9, an enzyme that breaks down the extracellular matrix surrounding cells.10npj Biofilms and Microbiomes. Bacterial vaginosis and health-associated bacteria modulate the immunometabolic landscape in 3D model of human cervix Think of the cervical surface as having a protective coating; BV bacteria strip that coating and loosen the structural scaffolding underneath. This makes it easier for HPV and other pathogens to reach deeper cell layers where they can establish infection.
Additionally, BV-associated bacteria produce enzymes like mucinase, sialidase, and protease at significantly elevated levels compared to what is found in women without vaginal infections. One case-control study found these three enzymes were roughly four to five times more elevated in women with bacterial infections than in women without dysplasia.11PubMed Central. Evaluation of microbial enzymes in normal and abnormal cervicovaginal fluids of cervical dysplasia: a case control study The changes in microbial metabolites also drive local inflammation, further damaging the epithelial and immune barriers of the cervix.12PubMed Central. Interactions between microbiota and cervical epithelial, immune, and mucus barrier
All of this tissue disruption and inflammation feeds back into what the Pap smear picks up: cells under stress, cells that look different from normal, cells that may be flagged as atypical even if no true precancerous transformation has occurred.
What Happens After an Abnormal Pap Linked to BV
If you get an abnormal Pap result and BV is suspected or confirmed, the clinical path forward depends on the severity of the abnormality. For mild results like ASC-US, many providers will treat the BV first and then repeat the Pap in a few months. The logic is sound: if inflammation was the culprit, clearing the infection should normalize the results.
For persistent inflammatory Pap smears that don’t resolve after treatment, further evaluation may be warranted. A prospective study examining women with persistent inflammatory Pap results who underwent colposcopy (a closer examination of the cervix with magnification) and biopsy found a wide range of underlying pathology. The most common biopsy finding was chronic cervicitis, a nonspecific inflammation, in about 29% of cases. But the study also found HPV-related lesions in about 21%, low-grade precancerous changes in roughly 15%, and high-grade precancerous changes in about 4% of cases.13CytoJournal. Colposcopic evaluation of cervix with persistent inflammatory Pap smear: A prospective analytical study The study even found two cases of carcinoma in situ and one case of invasive carcinoma hiding behind what appeared to be nonspecific inflammation on the Pap test.
These numbers reveal two things simultaneously. First, the vast majority of inflammatory Pap results are not cancer or even precancer. Second, a small but meaningful percentage of them do conceal serious pathology. This is why providers don’t simply dismiss inflammatory Pap results, even when BV seems like the obvious explanation. The BV may be the primary issue, or it may be a co-traveler alongside something more significant.
The Emotional Weight of an Abnormal Result
Abnormal Pap results generate real anxiety, and this dimension of the experience is worth acknowledging. A German survey of women who received abnormal screening results found that about 70% of women with an abnormal Pap smear reported being at least “rather concerned” about their findings. Roughly 27% described themselves as “severely concerned.”14PubMed Central. Psychological distress in cervical cancer screening: results from a German online survey This distress persists during the waiting period for follow-up testing and results.
Understanding that BV can cause or contribute to an abnormal result provides useful context. If your provider identifies BV as a likely contributor, knowing that treatment and a repeat Pap may resolve the abnormality can ease some of that worry. It doesn’t eliminate the need for follow-up, but it does reframe the result from “something might be seriously wrong” to “there’s an identifiable and treatable infection that could explain this.”
Why Treating BV Matters Beyond Symptoms
BV is often framed as a nuisance condition, especially since about half of women with it have no noticeable symptoms. The characteristic fishy odor and thin grayish discharge that many people associate with BV aren’t always present. This means BV can be silently influencing cervical health and Pap results without giving any obvious warning.
The longitudinal data on BV and HPV persistence adds urgency to treating BV even when it seems clinically mild. The study tracking HPV-positive women over time found that women without BV had clearance rates more than 20 percentage points higher than women with BV across both study cohorts.9PubMed Central. Bacterial vaginosis in microscopic examination of Pap smears in patients with high-risk HPV is associated with viral persistence and cytological progression in a longitudinal study That gap is substantial. Restoring a lactobacillus-dominant vaginal environment appears to improve the body’s ability to clear HPV on its own, which in turn reduces the likelihood of progressive Pap abnormalities.
Recurrence is the frustrating reality of BV, though. Standard antibiotic treatment with metronidazole or clindamycin clears the infection in most cases, but recurrence rates within a year are high, with some estimates suggesting more than half of treated women experience a return of BV. For women dealing with both BV and an abnormal Pap, this means staying on top of follow-up screening is especially important.
BV Alongside Other Vaginal Infections
BV doesn’t always arrive alone. Co-infections with Trichomonas vaginalis, a sexually transmitted parasite, are common and compound the problem. One study found BV in about 17% of Pap smears and Trichomonas in about 9%, with nearly 3% showing both infections simultaneously.1Nepal Medical College Journal. Study of Trichomonas Vaginalis and Bacterial Vaginosis in Pap smear at a Tertiary Health Care Centre of Nepal Trichomonas causes its own set of reactive cell changes on Pap smears, and when both infections are present, the inflammatory burden on the cervix increases and the likelihood of an abnormal result goes up.
The European study that found BV was not independently linked to major Pap abnormalities did find that aerobic vaginitis (a different type of vaginal inflammation involving aerobic bacteria) and microscopic signs of inflammation were independently associated with more serious cytological findings.6PubMed. Bacterial vaginosis, aerobic vaginitis, vaginal inflammation and major Pap smear abnormalities This underscores that the type of vaginal infection matters. Not all vaginal flora disruptions carry the same cervical risk, and BV may occupy a middle ground: clearly associated with mild Pap changes and HPV persistence, but less clearly an independent driver of high-grade abnormalities when considered apart from HPV.
When Cervical Screening Uses HPV Testing Instead of Pap Smears
An increasing number of screening programs around the world are moving toward primary HPV testing, either alone or alongside the Pap smear (known as co-testing). This shift matters for the BV question because HPV testing is a molecular test that detects viral DNA; it doesn’t rely on interpreting cell appearance under a microscope. That means BV-related inflammation can’t produce a false positive on an HPV test the way it can muddy a Pap smear reading.
However, the BV-HPV interaction still matters in an HPV-first screening world. If BV makes HPV harder to clear and increases the chance that a persistent HPV infection will progress to precancerous changes, then women with both BV and a positive HPV test are at higher risk of eventually developing an abnormal Pap result when the follow-up cytology is performed. The screening method changes, but the underlying biology doesn’t. Treating BV remains relevant regardless of which screening test your provider uses, because the goal isn’t just a clean test result but a healthier cervical environment that can fight off HPV more effectively.