The Complete Guide to the Vaginal Microbiome

The vaginal microbiome is the community of microbes — bacteria, yeast and other microorganisms — living inside the vagina. Also known as vaginal flora or microbiota, it works continuously to keep you healthy.

When it's disrupted, it can lead to conditions such as:

• Bacterial vaginosis (BV)
• Vulvovaginal candidiasis (VVC), aka yeast infections
• Urinary tract infection (UTI)
• Aerobic vaginitis (AV) and Desquamative Inflammatory Vaginitis (DIV)
• Ureaplasma infection
• Mycoplasma infection
• Cytolytic vaginosis (CV)

There's also a growing body of research that associates it with increased risk of acquiring sexually transmitted infections (STIs) and Human papillomavirus (HPV), as well as fertility, pregnancy and reproductive health outcomes.

This guide covers everything you need to know about what the vaginal microbiome is, how it protects you, what throws it off balance, and what you can do about it.

What is the vaginal microbiome?

Your vagina, like your gut, has its own resident community of microbes that it needs to be to be there for you to be healthy. What sets the vaginal microbiome apart from every other microbiome in the body is that diversity is not wanted here. Research consistently shows that, in general, a healthy vaginal microbiome is dominated by a single group of bacteria, collectively called Lactobacillus.

The five Community State Types

Every vaginal microbiome falls into one of five distinct categories, known as Community State Types (CSTs). Four of these five are Lactobacillus-dominant and broadly protective. The fifth is the catch-all category for the rest, which is generally considered disrupted.

CST I, dominated by Lactobacillus crispatus, is considered the most protective and stable. CST III, dominated by Lactobacillus iners, is protective too, but more fragile and can tip into CST IV under pressure. CST IV is defined by low Lactobacillus and a mix of other bacteria including Gardnerella vaginalis and Sneathia. It's this profile that's most strongly linked to infections, inflammation, and adverse reproductive outcomes.

There are very few edge cases that don’t follow this rule, with race and ethnicity documented as playing a role in what health may look like for you. Knowing the context and baseline of your vaginal microbiome is important for developing a personalized programme for getting you back on track when things go wrong. 

Why Lactobacillus is your first line of defence

Lactobacillus bacteria protect the vagina in three main ways. They:

• produce lactic acid, which keeps the vaginal environment acidic enough that most harmful bacteria simply can't survive there
• release natural antimicrobial compounds that actively fight off competing bacteria
• keep the immune system in a calm, stable state, meaning less inflammation, less irritation, and stronger defence against infection

Lactobacilli also generally occupy space and use resources so that other bacteria aren’t able to multiply. 

What can disrupt the vaginal microbiome?

While much steadier than the gut microbiome, the vaginal microbiome is still dynamic. It responds to hormonal shifts, lifestyle factors, and changes in the environment. Several common factors can alter its composition, with hormones being the primary driver. 

Hormonal changes

Estrogen, a key group of hormones for women, drives glycogen production in the vaginal lining. This glycogen is the fuel lactobacillus bacteria need to thrive. As estrogen levels shift, so, too, do lactobacillus levels. Vaginal dryness, discomfort, and recurring infections become common as a result. This is why several disruptions below follow a hormonal pattern: they are all, in different ways, estrogen stories.

Perimenopause and menopause

As estrogen declines in perimenopause and drops further after menopause, lactobacillus dominance declines with it. On its own, a more diverse vaginal microbiome is a normal shift that occurs with menopause and is not cause for concern. However, as the vaginal environment becomes less acidic and less protected, it can become more vulnerable to infection and inflammation.

Pregnancy

With increasing estrogen levels, the vaginal microbiome during pregnancy tends to be more lactobacillus-dominant and more stable than at other points in a woman's life. Research suggests this is a biological adaptation: a healthier microbiome during pregnancy helps protect against infection ascending from the vagina into the uterus at a time when the stakes are highest for both mother and baby. Lactobacillus crispatus dominance in early pregnancy in particular has been associated with more favorable pregnancy outcomes. 

Post-partum and breastfeeding

Delivery, regardless of whether it is vaginal or caesarean, triggers a sharp drop in estrogen and a loss of lactobacillus dominance. As in menopause, this is a normal part of the lifecourse; unlike menopause, this shift is temporary. However, research tracking women for a year after birth found that only around half had returned to a sturdy vaginal microbiome by the end of the first year. Breastfeeding, or lactation, extends the low-estrogen, low-lactobacillus state of the postpartum period.

Menstruation

Menses, aka your period, temporarily disrupts the vaginal microbiome in a predictable, recurring pattern. Research found that 58% of women had a disrupted vaginal microbiome during menses, falling to 32% in the follicular phase (the week after menstruation) and 29% in the luteal phase (the two weeks before the next period). For most women, the microbiome recovers as estrogen rises again throughout the cycle and the alkaline pH of menstrual blood is eliminated. For women with a more fragile microbiome, however, this monthly fluctuation can be enough to trigger a cycle of recurrent infections that never fully resolves between periods.

Contraception

The contraceptive method you use can meaningfully influence your vaginal microbiome, but the direction depends on the type. For example: 

• Consistent condom use provides great prevention of disruption and infection
• Hormonal contraception is associated with a reduced risk of microbiome disruption
• Nonhormonal contraceptive copper intrauterine devices (IUDs) have been associated with an increased risk of BV

If you have a history of recurrent infections, your contraceptive choice is worth discussing with your clinician in the context of your vaginal microbiome.

Antibiotics

Antibiotics, both oral and localized, are an essential part of multi-step protocols for bringing misbehaving vaginal microbiomes back under control. But they aren’t perfect. Even with antibiotics, BV came back within a year in nearly 70% of patients in one study, contributing to the recurrent cycle of disruption and infection. . There are a couple of reasons for this including depletion of all bacteria, the good as well as the bad, leading to an increased risk of things like yeast infections and other forms of disruption. The type of antibiotic, and the pre- and post-antibiotic care and supplementation tailored to the specific state of the vaginal microbiome are all important factors for breaking this cycle.

Sexual activity

Sexual activity can shift the composition of the vaginal microbiome by introducing new microbes. This is true across all partner genders, and particularly with new or multiple partners. This isn’t just about STIs. Often, a lactobacillus-rich starting point coupled with good practices is sufficient for ensuring that the vaginal microbiome bounces back after a disruption, at least for premenopausal women. New evidence also shows that treating yourself and your partner can successfully end recurrent infection cycles for many women with BV.

Hygiene products

You’ve heard the vagina is self-cleaning. And it is, for the most part. It requires no internal products to stay healthy when you’re already on track. Warm water on the vulva is usually all you need. Douching has been associated with increased risks of infection, pelvic inflammatory disease, and preterm birth, and is hypothesized to disrupt the vaginal microbial community by altering pH and creating an opportunity for pathogenic bacteria to colonize. Scented internal products, wipes, and washes marketed as freshening or balancing can cause the same disruption. Products such as these alter the vaginal pH and remove the lactobacillus layer that the vagina depends on for protection. If you notice an odor that concerns you, it is worth getting tested. The answer is almost always a microbiome imbalance, not a hygiene problem.

Psychosocial stress

Stress is one of the most overlooked disruptors of the vaginal microbiome. A large longitudinal study of 572 women found that a meaningful increase in perceived stress was associated with a 40% higher risk of developing a low-lactobacillus microbiome, and that women already in a disrupted state were less likely to recover protective lactobacillus dominance when stress levels were higher.

Research also documents what we know from experience already: that disrupted vaginal microbiomes can in turn cause further stress, especially when recurrent. It’s worth noting that while stress may be part of the picture, that doesn’t mean that, “It’s in your head.” Your symptoms should always be clinically investigated and never dismissed.

Smoking, alcohol & nutrition

Smokers are significantly more likely to have a disrupted vaginal microbiome than non-smokers. Alcohol consumption is linked to the vaginal microbiome, too. Early research also suggests that a balanced diet low in animal protein derived from red and processed meat and higher in plant protein, carbohydrates, starch, and fiber can be supportive of an optimal vaginal microbiome. In particular, α-linolenic acid, a plant-based omega-3 fatty acid found in foods like nuts, chia seeds, and flaxseeds has been highlighted as potentially beneficial as well. 

Health outcomes linked to vaginal microbiome disruption

Vaginal disruption, or vaginal dysbiosis, is associated with over 30 conditions. These can be thought of as falling into two categories: primary conditions that are directly caused by the disruption (like BV, AV, and DIV) and secondary complications that may arise from or be associated with the disruption (like yeast infections, increased risk of STIs, and UTIs). Some examples include the following:

Bacterial vaginosis (BV)

BV is the most prevalent vaginal condition in people of reproductive age globally. It occurs when lactobacillus populations fall and mixed anaerobic bacteria take hold. What makes BV particularly challenging is its recurrence rate: research shows that more than half of people relapse within six months of standard antibiotic treatment. Understanding your specific microbiome composition is one of the most important factors in breaking that cycle.

Yeast infections

A depleted lactobacillus population gives the yeast Candida (most commonly C. albicans) a clearer pathway to overgrowth. Research suggests that antibiotic-driven lactobacillus depletion is a direct precursor to Candida infections. Because a number of infections produce nearly identical symptoms to yeast infections, and because there are other types of yeast besides the common Candida, accurate testing is the only reliable way to distinguish them and treat them effectively.

STI susceptibility

A lactobacillus-dominant microbiome is a meaningful shield against STIs. Research finds that people with disruption are at an increased risk for acquiring STIs including HIV, chlamydia, gonorrhea, trichomoniasis, Mycoplasma genitalium, HPV, and herpes simplex virus type 2.

Pelvic inflammatory disease (PID)

Pelvic inflammatory disease (PID) occurs when bacteria from the vagina or cervix ascend into the upper reproductive tract (the uterus, fallopian tubes, and ovaries), causing infection and inflammation. Untreated, it can lead to chronic pelvic pain, ectopic pregnancy, and infertility. The link between a disrupted vaginal microbiome and PID is well-established; a  large longitudinal study found that women with BV, whether symptomatic or asymptomatic, had a meaningfully higher risk of developing PID.

Urinary tract infections (UTIs)

Because the vagina and urethra sit in such close proximity, a disrupted vaginal microbiome acts as a persistent reservoir for Escherichia coli and other UTI-causing microbes, repeatedly reseeding the urethra and driving the cycle of recurrent infection. It’s why UTIs can keep coming back if the vaginal microbiome is not addressed.

Fertility and pregnancy

The vaginal microbiome has been associated with both fertility and pregnancy outcomes. Research into preterm birth shows that women with undisrupted vaginal microbiomes, especially during the earlier stages of pregnancy, have better outcomes. Similarly, a systematic review and meta-analysis of 25 studies involving 6,835 patients undergoing in vitro fertilization found that vaginal disruption was present in around 19% of patients. This disruption was associated with a lower clinical pregnancy rate and a 49% higher risk of early pregnancy loss.

Signs your microbiome may be disrupted

Your body will often let you know something’s not right. Symptoms, when they do appear, can include:

• Unusual discharge (gray, white, yellow, or watery in appearance)
• A strong or fishy smell, often more noticeable after sex
• Vaginal itching, burning, or irritation
• Pain or discomfort during sex
• A burning sensation when you urinate

Because these symptoms overlap across several different conditions (BV, yeast infections, aerobic vaginitis, cytolytic vaginosis, various STIs, and more), symptoms alone are rarely a reliable guide to what's actually going on. Sometimes, however, your body won’t let you know. There will be no symptoms. For example, up to 84% of people with bacterial vaginosis have no symptoms and, according to the CDC, around 75% of people with chlamydia are completely asymptomatic. Disruption can be entirely silent, which is why testing is so important. And testing the right way even more so.

Why standard tests often miss the full picture

Standard vaginal swabs use culture-based methods or targeted polymerase chain reaction (PCR) panels. They identify a handful of specific predetermined organisms only. Comprehensive microbiome testing using next-generation sequencing (NGS) identifies all the microbial DNA in a sample simultaneously, screening for over 10,000+ microbes and identifying all the bacteria and yeast from a single swab, including organisms that standard panels simply don't screen for.

For people with recurrent infections or unexplained symptoms, this level of detail makes the difference between knowing and guessing.

What supports a healthy vaginal microbiome

There are many things we can do to support a healthy microbiome. Here are some of the most effective:

Keep the vaginal environment simple

Vaginal care should be kept simple. No scented products, internal soaps or douching (unless specifically recommended by your physician).

Get the right antimicrobial

Not all antibiotics or antifungals will work in the same way on different vaginal microbiome profiles. In fact, antibiotics can’t cure a yeast infection, and antifungals do nothing for a bacterial infection. Knowing what you’re dealing with and selecting the right treatment, for the right duration, is crucial.

Consider vaginal probiotics, with the right strain

Strain specificity matters here. Taking the right strain at the right time, informed by testing to understand your baseline microbiome composition, will give you the most reliable outcome.

Use condoms consistently, if you're into that sort of thing

Consistent condom use reduces exposure to new microorganisms and is one of the most well-evidenced ways to maintain microbiome stability, particularly with new or multiple partners.

Get a precise diagnosis before treating

Treating symptoms without knowing their cause is one of the most reliable routes to a cycle of recurring infections. Comprehensive microbiome testing gives you specific information to act on, rather than a best guess.

The bottom line

Your vaginal microbiome is a significant part of your health. The research is consistent: a healthy vaginal microbiome protects against infections, lowers STI risk, and plays a meaningful role in fertility and pregnancy outcomes. Understanding what's happening in your microbiome gives you the power to make informed decisions about your health.