‘The Microbiome Is a Bit Like a Forest’: Understanding Vaginal Bacteria and Women’s Health

The vaginal microbiome, a complex ecosystem of bacteria, fungi, and viruses, has long been overshadowed by studies of gut microbes. Yet scientists now recognize its crucial role in women’s health, influencing susceptibility to infections, reproductive outcomes, and potentially even cancer risk.

The Role of Lactobacillus in Health

During puberty, rising oestrogen levels encourage the colonization of beneficial bacteria known as Lactobacillus, which can help prevent infections by competing with harmful microbes and producing lactic acid. “They crowd out pathogens, competing with them for nutrients and space,” explains Chrysi Sergaki, head of microbiome at the UK’s Medicines and Healthcare products Regulatory Agency (MHRA). Lactobacillus also modulates local immune responses and produces natural antimicrobial substances, creating a hostile environment for harmful bacteria.

When this balance is disrupted, a condition known as vaginal dysbiosis can occur, increasing the risk of bacterial vaginosis (BV), thrush, urinary tract infections (UTIs), and sexually transmitted infections (STIs) such as HIV. Laura Goodfellow, a clinical lecturer in women’s and children’s health at the University of Liverpool, notes that lower levels of Lactobacillus correlate with higher HIV susceptibility in high-risk populations, and can also impair the clearance of human papillomavirus (HPV), a major contributor to cervical, vulval, and vaginal cancers.

“The microbiome is a bit like a forest,” Goodfellow explains. “A healthy ecosystem resists colonization by harmful microbes. If the microbiome is disrupted, pathogens can establish more easily.”

Implications for Fertility and Pregnancy

The vaginal microbiome also appears to influence reproductive outcomes. Women with low Lactobacillus levels face higher risks of miscarriage, ectopic pregnancy, and preterm birth. Bifidobacterium, another beneficial bacterium present in smaller numbers, may also reduce the likelihood of preterm delivery. Dysbiosis has additionally been linked to reduced success in fertility treatments such as IVF.

One proposed mechanism involves inflammation. While some inflammation is necessary for immune defense, excessive vaginal or placental inflammation may trigger preterm labor or complicate conception. “Women who have Lactobacillus have lower levels of inflammatory proteins within vaginal fluid,” Goodfellow says. “Dysbiosis appears to increase inflammation, which in some cases can contribute to adverse pregnancy outcomes.”

Lactobacillus is similarly recognized for its anti-inflammatory effects in the gut, highlighting the systemic importance of maintaining beneficial microbial communities. The presence of pathogens from STIs such as chlamydia or gonorrhea further underscores the protective role of a healthy microbiome in preventing pregnancy complications and reproductive tract cancers.

Toward Personalized Microbiome Medicine

Research teams are exploring interventions to enhance the vaginal microbiome. At Imperial College London, a clinical trial is testing Lactin-V, a probiotic containing Lactobacillus crispatus, to reduce preterm birth rates among high-risk women. Early results suggest that supplementation can shift the vaginal microbiome toward Lactobacillus dominance. Studies also indicate that blood type may influence microbiome composition, with type A associated with higher Lactobacillus levels and a lower risk of preterm birth, while types B and O may carry slightly higher risks.

Scientists are investigating whether Lactin-V might also protect women at high risk of HIV and are advocating for microbiome-based diagnostic tools. Such tests could non-invasively assess a woman’s microbial composition, predicting risks for miscarriage, infertility, preterm birth, or cervical cancer, and guiding personalized preventive strategies.

Protecting the Vaginal Microbiome

Maintaining a healthy vaginal microbiome involves both lifestyle and behavioral considerations. Practices such as vaginal douching can disrupt microbial balance, increasing the risk of BV, preterm birth, and pelvic inflammatory disease, which can impair fertility. Similarly, feminine hygiene products like gels, sprays, or wipes may damage the delicate ecosystem.

Sexually active individuals may benefit from barrier contraceptives, as semen can alter vaginal microbial balance, whereas condom use has been linked to higher Lactobacillus prevalence. Nutrition also plays a role: deficiencies in vitamins A, C, D, E, β-carotene, folate, and calcium, as well as diets high in fat or obesity, are associated with less optimal microbial communities. Smoking is another risk factor, with studies showing increased BV prevalence and reduced Lactobacillus in smokers compared with non-smokers, alongside higher risks of preterm birth.

“Eating plenty of leafy green vegetables, getting enough sleep, drinking enough water—all these general practices that improve overall health will likely benefit the vaginal microbiome too,” Goodfellow adds.

Looking Ahead

As research advances, the vaginal microbiome is increasingly seen as a critical component of reproductive and overall health. From preventing infections and supporting successful pregnancies to reducing cancer risk, the ecosystem of microbes in the vagina is proving to be as essential as its better-studied gut counterpart. Emerging diagnostics, probiotics, and personalized interventions could mark a new era in women’s healthcare, with the potential to transform reproductive medicine and improve health outcomes on a global scale.