Your Inner Landscape, Revealed: The 5 Types of Vaginal Microbiomes

We humans love to categorize ourselves—just ask your friend, the Gemini, INTJ, Life Path Number 8 Manifesting Generator. Some may see these categories as frivolous, but others use them to excavate their innate desires, personality quirks, and relationship tendencies. 

And it turns out, certain categorizations are important within the medical context, too. Thanks to evolving research in the women’s health space, for example, we now know that there are five distinct “types” of vaginal microbiomes—and each says something different about its host’s vulnerability to infection, fertility complications, and more. 

So, in the name of useful self-categorization, here’s an overview of the five types of vaginal microbiomes identified by research and what each one says about its host.

Science with us—nerdy reads for your inbox biome¹

Sign Up

¹By signing up, you consent to receive Seed emails.

Your Vaginal Microbiome, Explained

The vaginal microbiome (VMB) is a group of microorganisms that reside in the vagina. It’s populated by a bustling community of microbes; primarily bacteria, though some yeasts can also set up shop there.^1,2 Like human communities, different residents of the vaginal microbiome carry out unique activities, ideally working together to help maintain the status quo. 

When all community members exist in harmony with the surrounding environment (the vagina), the vaginal microbiome is in a steady state of homeostasis.³ An ideal vaginal environment for a woman of reproductive age is somewhat acidic, with a pH of around between 3.8 and 5.0 (though it may shift slightly depending on where you are in your cycle or menopause transition).⁴ This environment tends to be protective against intruders that can carry infections. 

Many common triggers (think: antibiotics, sex, lubrication, exercise, douching… the list goes on) can throw off this internal ecosystem. Scientists call this state of disturbance “dysbiosis.”³ Dysbiosis makes us more susceptible to a variety of vaginal health concerns, including yeast infections, bacterial vaginosis (BV), preterm birth (PTB), and increased risk of sexually transmitted infections.⁵

Throughout our lives, our vaginal microbiomes are bound to move between states of homeostasis and dysbiosis. This process is natural and to be expected (so no, it’s not your fault if you deal with recurring symptoms like yeast infections or BV). However, scientists have uncovered that some vaginal microbiome compositions are inherently more resilient to dysbiosis than others.

The 5 Community State Types (CSTs)

Since 1892, scientists have been aware that Lactobacillus, a genus of lactic acid-producing bacteria, can be found in most healthy vaginas.⁶ But, thanks to sexist science and trepidation around conducting research on women, they didn’t know much beyond that.  

It wasn’t until the early 2010s that a clearer picture of the vaginal microbiome, in all of its intricately complex glory, emerged in a groundbreaking study titled Vaginal microbiome of reproductive-age women. Helmed by Jacques Ravel, Ph.D., a leading expert in vaginal microbiome science, the study discovered five distinct “community state types,” or CSTs, among 396 asymptomatic, reproductive-age women of different ethnicities. (This first-of-its kind self-collection study was staggering in its scope, amassing a rich dataset of nearly 900,000 rRNA gene sequences—but that’s a story for another time.)¹

It turns out that there were a few different types, or species, of Lactobacillus that tended to be most prevalent in vaginal microbiomes. You can think of the different Lactobacillus species as microbial cousins. They share a family name and similar genetics, but they have different first names, abilities, and preferences for what they need to thrive. Dr. Ravel found that each CST’s susceptibility to dysbiosis hinged on its dominant species of Lactobacillus.

Follow-up studies have continued to confirm these five major CSTs across populations, and have further clarified some general properties of each. Let’s explore:⁷

CST I: Lactobacillus crispatus dominant

Dr. Ravel and his team found that the vaginal microbiome will ideally have one species of Lactobacillus that keeps the entire ecosystem in homeostasis. The first CST, CST I, is dominated by the bacterial species Lactobacillus crispatus. When L. crispatus is dominant, the vagina usually has a pH less than 4.5, and a low Nugent score.⁷ The Nugent score is a research tool that flags abnormal flora in the vagina—so a low score is a sign that you are not experiencing BV.

At this point, scientists believe CST I is the most stable and protective CST.⁶ In fact, having a CST I is such a strong predictor of positive outcomes that it is often considered a proxy for optimal vaginal health. Here’s the kicker, though: only 10% of women have it.⁸

CST II: Lactobacillus gasseri dominant

CST II is dominated by the bacterial species Lactobacillus gasseri. This is a relatively rare CST, and researchers are still trying to parse out its unique qualities.⁶ When L. gasseri is dominant, the vagina is more likely to have a pH in the 4.5 to 5.5 range, meaning it’s less acidic.⁷ And since acid generally keeps out undesirable microbes, which can cause infections and inflammation, CST II is not as protective as CST I.  

CST V: Lactobacillus jensenii dominant

Similar to CST II, CST V is a rarer and lesser-understood VMB state type.¹ In general, the CST V state is associated with an acidic pH below 4.5, and a low chance of dysbiosis, as measured by a Nugent score.⁷ Still, it’s not considered as protective as CST I either. 

CST III: Lactobacillus iners dominant

CST III is a common VMB state across all ethnicities, and about 34% of women from Dr. Ravel’s initial research had it.¹ It’s dominated by a diverse bacterial species called Lactobacillus iners and associated with a vaginal pH above 4.4 (meaning a less acidic environment).¹ 

The strange thing about CST III is that it is more likely to fluctuate to Lactobacillus-deficient states compared to CST I.⁹ This somewhat fickle strain is not solidly categorized as either harmful or beneficial—it can swing either way.¹⁰ Research suggests that L. iners is a transitional species that colonizes after the vaginal environment is disturbed and all in all, CST III seems to offer less protection against dysbiosis.^6,11

Given the ubiquity of this dominant Lactobacillus species, scientists are investigating why it tends to be less protective against infection than its cousins. So far, they’ve identified that L. iners do not produce hydrogen peroxide (H₂O₂), whereas most other vaginal lactobacilli can produce it.⁶ Hydrogen peroxide is toxic to many bacteria and could therefore theoretically keep other, potentially harmful microbes from thriving in the vagina.

However, whether or not this is in fact the key difference that causes decreased protection is still under debate. For now, we can say there are likely multiple contributing factors that make CST III less protective than CST I.⁶

CST IV: Non Lactobacillus dominated 

CST IV is the final type, and it’s the only one that is not dominated by a Lactobacillus species. Lactobacillus species may be present in this CST, but they are not as abundant relative to the other community members.¹ 

Without a dominant Lactobacillus species protecting the vagina, women with this CST are the most vulnerable to dysbiosis.^6,9 And unfortunately, time and time again, CST IV has been shown to be one of the most prevalent vaginal types among women, affecting anywhere from ~37.1% to 42.8% of those sampled at some point of their cycle.^6,12,13

Some people with this unstable type may experience symptoms such as abnormal discharge or vaginal odor. However, others will be completely asymptomatic, and not realize they could be more vulnerable to issues like bacterial vaginosis, yeast infections, STI acquisition, and pregnancy and birth complications.⁶

As Dr. Ravel put it in a 2016 presentation, “Low stability equals low resilience equals increased risk.” 

Remember: Your Type Is Always Changing

Unlike your zodiac sign or Myers-Briggs Type, your Community State Type ebbs and flows over time. Again, your menstruation status, sex life, and lifestyle can all cause your vaginal ecosystem to fluctuate between CSTs.  

So if you currently have signs of a CST IV type, that’s not to say you’ll have it forever. While you may be predisposed to a certain type, you can move the needle toward a more optimal, steady-state vaginal microbiome through lifestyle changes.

Eating a higher-fiber, low-fat, nutrient-dense diet (high-fat diets have been associated with BV), being mindful of antibiotic use, and limiting inflammatory inputs like cigarettes, sugar, and alcohol may help support protective microbial flora.^14-18 Pescatarian diets have also been associated with an increase of L. crispatus in some ongoing research, while an increased intake of micronutrients such as folate, vitamin A, and calcium may reduce the risk of BV.^15,17

Vaginal probiotics can also help colonize the vaginal microbiome with beneficial bacteria. As mentioned earlier, CST I is a protective state for vaginal microbiomes, and it’s dominated by L. crispatus. So, all signs point to L. crispatus being the ideal microbe to protect your VMB. 

But it’s not quite that simple: The specific strain of L. crispatus matters, too. If different Lactobacillus species are cousins, then different strains within a single species are siblings. They are even more closely related, but they still have subtle differences that can make them totally unique. Take E. coli, for example. This species has hundreds of strains, many of which live in our intestines and are considered normal—but at least 200 that are pathogenic and cause severe illness.

In 2020, a landmark study provided the research world with a detailed map of the vaginal microbiome landscape, down to this strain level, called the human vaginal non-redundant gene catalog (VIRGO).¹⁹ Through this genomic mapping exercise, researchers found that “a woman’s vaginal bacterial populations are routinely comprised of more than one strain of most species.” This study then went on to identify the strains of L. crispatus that are most protective in the vaginal microbiome. So, if you’re in the market for a vaginal probiotic that actually works, you’ll want to look for one that contains these gold-standard L. crispatus strains.

Let’s Move Towards CST I Together

Up to 90% of women have unstable vaginal microbial makeups and run a higher risk of vaginal dysbiosis than those who have CST I. Luckily, your CST is ever-evolving. Keeping up with certain lifestyle habits and taking a well-formulated vaginal probiotic, can help you move towards this ideal “type” once and for all.⁸