10% of Women Have Unclassified Vaginal Microbiomes

Despite playing a vital role in women’s health, research surrounding the vaginal microbiome is largely limited.  A new study, led by researchers from the University of Antwerp and published in Trends in Microbiology, aims to change that.

Their findings challenge traditional classifications of vaginal microbiota and highlight the need for global collaboration to address geographical biases and improve women’s health research worldwide.

The vaginal microbiome is a complex and evolving ecosystem

The vaginal microbiome is traditionally composed of a diverse community of microorganisms, including bacteria, fungi and viruses, which interact with the host to maintain health. In many women, lactobacilli dominate, particularly Lactobacillus crispatus, L. iners, L. gasseri and L. jensenii. These bacteria produce lactic acid, hydrogen peroxide and antimicrobial compounds that help maintain an acidic vaginal pH, creating an environment that prevents harmful pathogens from proliferating.

When this delicate balance is disrupted, women become more susceptible to various health issues. One example is bacterial vaginosis (BV), characterized by a decrease in lactobacilli populations and an overgrowth of anaerobic bacteria. BV has been linked to an increased risk of preterm labor and delivery of babies that are small for gestational age. Dysbiosis can also lead to urinary tract infections and other complications.

Understanding the role of these microbial communities is vital for advancing women’s health and yet research in this area is limited. Defining a "healthy" vaginal microbiome can also present challenges, as traditional classifications may not capture its full complexity.

“Western medicine, to this day, assumes an androcentric perspective at the expense of women,” said the international team of researchers, led by corresponding author Dr. Sarah Lebeer, a research professor at the University of Antwerp.

While lactobacilli dominance is often associated with vaginal health, some women naturally harbor different bacterial communities without experiencing adverse health effects, highlighting the complexity of what constitutes a "healthy" vaginal microbiome. Many women may not fit within the standard categories of vaginal microbiota composition, suggesting that the current understanding may be incomplete. Additionally, 9 out of 10 studies only include participants from one continent, resulting in large geographical gaps in knowledge.

"Women’s health is essential to global societal and economic wellbeing, yet health disparities remain prevalent. Women’s bodies, and knowledge concerning their health have been neglected, controlled and persecuted for centuries, resulting in a health disparity that persists today," said the authors.

Understanding the vaginal microbiome requires large-scale, inclusive research that goes beyond traditional clinical studies, which is precisely what Lebeer and the team aimed to achieve. 

A citizen-science approach to women’s health

Through a collaborative and citizen-driven approach, the researchers sought to fill the gaps in vaginal microbiome data by involving thousands of participants across multiple continents through the Isala Sisterhood initiative. Originally launched in Belgium, the project encouraged participants to act as active contributors rather than passive subjects. Its success led to its expansion into a global network, with sister projects now operating in regions such as North America, South America, Africa and Asia.

Women were invited to participate in research by donating self-collected vaginal swabs, answering detailed lifestyle and health questionnaires and engaging in discussions about vaginal health. These samples were then analyzed using advanced microbiome sequencing techniques, such as 16S rRNA amplicon sequencing and metagenomics, to characterize bacterial diversity and identify previously unrecognized microbial compositions. The team compiled the results from the Isala Sisterhood and other similar initiatives alongside almost 100 years of research.

They found that over 10% of Belgian participants did not fit within the standard microbiome classifications commonly used in vaginal health research. Traditionally, vaginal microbiomes are grouped into five community state types, each dominated by specific bacterial species. However, the Isala study found that some women exhibited mixed bacterial profiles that did not conform to these predefined categories. This finding challenges the existing understanding of what constitutes a "healthy" vaginal microbiome and suggests that microbial diversity may be broader than previously thought.

The researchers reaffirmed previous findings that a reduction in lactobacilli species can lead to an overgrowth of anaerobic bacteria. This imbalance was linked to various health conditions including BV and an increased susceptibility to sexually transmitted infections.

Another major focus of the study was addressing geographical biases in vaginal microbiome research. Historically, microbiome studies have been conducted in high-income countries, primarily North America and Europe. As a result, the microbiome profiles of women from underrepresented regions – such as sub-Saharan Africa, South America and parts of Asia – remain poorly understood. The study highlighted that vaginal microbiomes vary significantly across geographical regions and are shaped by a combination of genetic, environmental and lifestyle factors. Practices such as vaginal douching, hygiene products, diet and menstrual care methods can influence microbial composition, potentially affecting women’s health outcomes in different parts of the world.

The future of vaginal health

Current treatments for conditions such as BV rely heavily on antibiotics, which have limited long-term efficacy and recurrence rates as high as 60%. The study highlights the potential of vaginal live biotherapeutic products – treatments that use beneficial bacteria to restore and maintain a healthy vaginal microbiome. By repopulating the vagina with protective lactobacilli species, these microbiome-based therapies could offer more sustainable and effective alternatives to antibiotics, reducing the risk of antimicrobial resistance and treatment failure.

However, as research advances, the authors note that the vaginal microbiome is shaped by more than just biology. To create effective and inclusive health interventions, scientists must incorporate diverse influences, such as the differences in diet and sexual habits across regions and communities, into their research.

“To promote better preventive, diagnostic and therapeutic strategies for women affected by conditions associated with the vaginal microbiota, more research on the functions and diversity of the vaginal microbiota is urgently needed in different parts of the world. This way, we can better understand what a healthy vaginal microbiome looks like in each geographical location,” the team concluded. 

Reference: Condori-Catachura S, Ahannach S, Ticlla M, et al. Diversity in women and their vaginal microbiota. Trends Microbiol. 2025. doi: 10.1016/j.tim.2024.12.012

This article is a rework of a press release issued by Cell. Material has been edited for length and content.