Skip to content
Vaginal Microbiome Community State Types (CSTs) Explained

Vaginal Microbiome Community State Types (CSTs) Explained

A woman's vagina is home to billions of bacteria. Researchers have found that these bacteria tend to fall into a small number of patterns, known as Community State Types, or CSTs. 

Which type you have can impact your daily risk of undesirable, infection like symptoms in the vagina and bladder, but also if relevant, pregnancy and fertility outcomes. This blog explains the five types of vaginal microbial categories (and sub categories), and how you can use our reporting to see which one you may fall into.

What are Community State Types (CSTs)?

In 2011, researchers looked at the vaginal bacteria of nearly 400 women and found they fell into five groups.¹ Four of the groups were dominated by one type of Lactobacillus. The fifth had lots of different bacteria and very few lactobacilli.

Lactobacilli matter because they make the vaginal canal acidic at a healthy pH of 3.7 to 4.5, making it harder for unwanted bacteria to take hold.

The five CST types

  • Type 1: Lactobacillus crispatus. One of the most common types. It has the lowest pH of the five, at 4.5 or under.² It's usually protective, and women with this type have a lower risk of preterm birth if they become pregnant.³˒⁴
  • Type 2: Lactobacillus gasseri. Less common but linked to good health like CST type 1. It stays stable over time and is associated with a lower risk of sexually transmitted infections and preterm birth.³˒⁶˒⁷
  • Type 3: Lactobacillus iners. Also one of the most common types. It's usually seen as healthy, but L. iners makes less lactic acid than L. crispatus, so the environment is less stable.¹˒⁵ Women with this type have a higher chance of bacterial vaginosis (BV) than women with type 1,⁸ and L. iners can increase after antibiotics. For some women type 3 stays stable. For others it can tip into imbalance.
  • Type 4: Diverse bacteria. Few lactobacilli, a higher pH and lots of different bacteria. These communities are less stable and more likely to host harmful microbes.⁹
    • Types 4A and 4B are linked to BV and contain bacteria such as Gardnerella vaginalis, Fannyhessea vaginae, BVAB1 and Prevotella species.¹˒⁵ 
    • Type 4C is more varied, and can be dominated by Prevotella, Streptococcus, Enterococcus, Bifidobacterium or Staphylococcus. Some women have type 4 without any symptoms,¹ so results are best read alongside symptoms. 
  • Type 5: Lactobacillus jensenii. Rare, but linked to good health. L. jensenii helps keep the pH low and protect against infection,¹⁰˒¹¹˒¹² and women with this type have a lower risk of preterm birth.¹³

 

Your CST can change 

Your community state type isn't fixed for life. After menopause, falling oestrogen means less glycogen for lactobacilli to feed on, so lactobacillus levels tend to drop, the pH rises and diverse, type 4 style communities become more common. During pregnancy, the microbiome tends to stay lactobacillus dominated. Antibiotics, lifestyle factors, immune health and partners can also influence the vaginal microbiome and the CST. 

It also differs between women. In the original study, type 4 was found in about 1 in 10 White women and 1 in 5 Asian women. It was found in about 4 in 10 Black and Hispanic women.

Symptoms are more common when the microbiome is in a dysbiotic state, such as type 4. Women with an imbalance are more likely to notice unusual discharge, odour, itching or burning, or to get repeated infections. But not every woman with an imbalance has symptoms. Many feel completely fine, which is why an imbalance can go unnoticed for a long time. Sometimes the only way to find it is a vaginal microbiome test, which can show what's going on even when nothing feels wrong.CSTs and symptoms

Why does your CST type matter?

In general, the more lactobacillus dominant the microbiome, the better the outcomes, and the type of lactobacillus makes a difference.

For infections, types 1, 2 and 5 are usually protective, type 3 carries a higher risk of BV, and type 4 is the least stable. For pregnancy, types 1, 2 and 5 are linked to a lower risk of preterm birth.
For fertility, studies of women having IVF have found that those with a lactobacillus dominant microbiome, especially L. crispatus, tend to have higher rates of implantation, pregnancy and live birth.¹⁴˒¹⁵

Women without lactobacillus dominance tend to do less well. Not every study agrees, and your type doesn't decide whether you'll conceive. It's one piece of a bigger picture.

Whats your CST? 

Our Vaginal Microbiome Test can help you to understand your CST type.   

  • Our report measures around 50 bacterial and yeast species and shows how much of each was found. Community state types are defined by which bacteria dominate, so your report gives you what you need to see where you sit.
  • The beneficial bacteria table lists 14 protective species. The one with the highest number shows which lactobacillus dominates (if any). 
  • Top 5 microbes shows the most abundant species on your swab.
  • The beneficial bacteria score shows how much of your microbiome is acid-producing bacteria. Over 95% is a healthy score.
  • Dysbiosis markers include a flag if L. iners has been detected, as it's a weaker strain.
  • Vaginal pH shows whether you're in the healthy range of 3.7 to 4.5.

Please remember, our test is a screening tool, not a diagnosis, and is best discussed with your healthcare practitioner to understand the implications for your specific health journey. 

References

  1. Ravel J, Gajer P, Abdo Z, et al (2011). Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1002611107
  2. Witkin SS, Mendes-Soares H, Linhares IM, et al (2013). Influence of vaginal bacteria and D- and L-lactic acid isomers on vaginal extracellular matrix metalloproteinase inducer: implications for protection against upper genital tract infections. mBio. doi: 10.1128/mBio.00460-13
  3. Kindinger LM, Bennett PR, Lee YS, et al (2017). The interaction between vaginal microbiota, cervical length, and vaginal progesterone treatment for preterm birth risk. Microbiome. doi: 10.1186/s40168-016-0223-9
  4. Petricevic L, Domig KJ, Nierscher FJ, et al (2014). Characterisation of the vaginal Lactobacillus microbiota associated with preterm delivery. Scientific Reports. doi: 10.1038/srep05136
  5. France MT, Ma B, Gajer P, et al (2020). VALENCIA: a nearest centroid classification method for vaginal microbial communities based on composition. Microbiome. doi: 10.1186/s40168-020-00934-6
  6. Spurbeck RR & Arvidson CG (2010). Lactobacillus jensenii surface-associated proteins inhibit Neisseria gonorrhoeae adherence to epithelial cells. Infection and Immunity. doi: 10.1128/IAI.01200-09
  7. Phukan N, Brooks AES & Simoes-Barbosa A (2018). A cell surface aggregation-promoting factor from Lactobacillus gasseri contributes to inhibition of Trichomonas vaginalis adhesion to human vaginal ectocervical cells. Infection and Immunity. doi: 10.1128/IAI.00907-17
  8. Carter KA, Fischer MD, Petrova MI & Balkus JE (2023). Epidemiologic evidence on the role of Lactobacillus iners in sexually transmitted infections and bacterial vaginosis: a series of systematic reviews and meta-analyses. Sexually Transmitted Diseases. doi: 10.1097/OLQ.0000000000001744
  9. DiGiulio DB, Callahan BJ, McMurdie PJ, et al (2015). Temporal and spatial variation of the human microbiota during pregnancy. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1502875112
  10. Morais IMC, Cordeiro AL, Teixeira GS, et al (2017). Biological and physicochemical properties of biosurfactants produced by Lactobacillus jensenii P6A and Lactobacillus gasseri P65. Microbial Cell Factories. doi: 10.1186/s12934-017-0769-7
  11. Atassi F, Brassart D, Grob P, Graf F & Servin AL (2006). Lactobacillus strains isolated from the vaginal microbiota of healthy women inhibit Prevotella bivia and Gardnerella vaginalis in coculture and cell culture. FEMS Immunology & Medical Microbiology. doi: 10.1111/j.1574-695X.2006.00162.x
  12. Gil NF, Martinez RCR, Gomes BC, Nomizo A & De Martinis ECP (2010). Vaginal lactobacilli as potential probiotics against Candida spp. Brazilian Journal of Microbiology. doi: 10.1590/S1517-83822010000100002
  13. Freitas AC & Hill JE (2017). Quantification, isolation and characterization of Bifidobacterium from the vaginal microbiomes of reproductive aged women. Anaerobe. doi: 10.1016/j.anaerobe.2017.05.012
  14. Moreno I, Codoñer FM, Vilella F, et al (2016). Evidence that the endometrial microbiota has an effect on implantation success or failure. American Journal of Obstetrics and Gynecology. doi: 10.1016/j.ajog.2016.09.075
  15. Koedooder R, Singer M, Schoenmakers S, et al (2019). The vaginal microbiome as a predictor for outcome of in vitro fertilization with or without intracytoplasmic sperm injection: a prospective study. Human Reproduction. doi: 10.1093/humrep/dez065

Pelvic Relief is the trading name of Elgenia Health Ltd, a company registered in England and Wales under Company Number 09833237 and whose Registered Address is at Upper Brockington, Bredenbury, Bromyard, Herefordshire HR7 4TH, VAT Number 227118426. ©Elgenia Health Ltd, 2026. Pelvic Relief® is a registered trade mark of Elgenia Health Ltd.