What Is the Vaginal Microbiome, and Why Does It Matter?

What is the vaginal microbiome?

The vaginal microbiome is the mix of bacteria, and smaller numbers of fungi and other microbes, living on the walls of the vagina. Like your gut, it is unique to you and it changes over time. Unlike your gut, a healthy vaginal microbiome usually contains only a small number of species.

A landmark 2011 study of almost 400 women found that most vaginal communities fell into five broad groups, called community state types ². Four were each dominated by a single Lactobacillus species:

• Lactobacillus crispatus
• Lactobacillus iners
• Lactobacillus gasseri
• Lactobacillus jensenii

The fifth group had far fewer lactobacilli and a wider mix of other bacteria, many of which do not need oxygen to grow (anaerobes). This group also tended to have a higher pH ².

Researchers now see these groups as a useful map rather than a strict rulebook. Your community can shift from one type to another, and what is normal varies between people ³.

What does the vaginal microbiome do?

• Keeps the environment acidic: Lactobacillus bacteria produce lactic acid, which keeps vaginal pH low, usually below about 4.5 ¹⁴.
• Helps defend against infection: that acidity, along with other substances lactobacilli make, helps limit the growth of harmful bacteria and yeast ¹⁴.
• Is linked to reproductive health: communities with plenty of lactobacilli are associated with better outcomes in fertility and pregnancy, although research is still developing ⁴.
• Adapts through life: it responds to oestrogen, so it shifts with puberty, the menstrual cycle, pregnancy and menopause ¹.

What makes the vaginal microbiome different from the gut?

In the gut, a wide variety of bacteria is generally a sign of good health. In the vagina, the opposite is usually true.

A healthy vaginal microbiome is typically low in diversity, with one or two Lactobacillus species doing most of the work ²³. When those lactobacilli decline and many different bacteria move in, the environment becomes less acidic, and that pattern is the one most often linked to bacterial vaginosis (BV) ²³.

So "more diverse" does not mean "healthier" here.

That said, low Lactobacillus levels are not automatically a problem. Some people with more mixed communities have no symptoms at all and feel completely well ².

What is a balanced vs imbalanced vaginal microbiome?

A balanced vaginal microbiome is usually:

• Dominated by Lactobacillus
• Acidic, with a low pH
• Stable, without recurring symptoms

An imbalanced microbiome, sometimes called vaginal dysbiosis, is when protective lactobacilli decline, other bacteria increase and pH rises. This can make the vagina more vulnerable to infection ³⁴.

The best known example is BV, which the NHS describes as a common cause of unusual vaginal discharge caused by a change in the natural balance of bacteria ⁵. Signs can include a thin, greyish-white discharge with a strong fishy smell, especially after sex. Half of women with BV have no symptoms at all ⁵.

→ 6 Signs of an Imbalanced Vaginal Microbiome (and What They Mean)

Everyday things can tip the balance. These include hormonal changes, sex with a new partner and using perfumed products in or around the vagina ¹⁵.

→ What Causes Vaginal Imbalance

How does the vaginal microbiome change through life?

Oestrogen is the main driver. It thickens the vaginal lining and increases the glycogen stored there, which is the food lactobacilli depend on ¹.

• Childhood: oestrogen is low, so lactobacilli are scarce and the environment is closer to neutral.
• Puberty and the reproductive years: rising oestrogen lets lactobacilli flourish and pH drops.
• Pregnancy: the community often becomes more stable and Lactobacillus dominated ¹.
• Menopause: as oestrogen falls, lactobacilli tend to decline and pH rises, which can go hand in hand with dryness and irritation ⁴.

→ The Vaginal Microbiome Through Life

Why does the vaginal microbiome matter?

For most people, the most noticeable effect is day-to-day comfort. A stable, acidic environment helps protect against infections such as BV and thrush, which can cause discharge, odour, itching and soreness ⁵.

Research is also exploring wider links with women's health. A 2025 review co-authored by scientists at the UK's Medicines and Healthcare products Regulatory Agency (MHRA) brought together evidence connecting the vaginal microbiome with ⁴:

• Bacterial vaginosis, which affects an estimated 23 to 29% of women of reproductive age worldwide
• Fertility, including lower IVF success where lactobacilli are low
• Pregnancy, including a higher risk of preterm birth and early miscarriage with low-Lactobacillus communities
• Menopause, where changes in vaginal bacteria may relate to symptoms such as dryness

The authors are clear that most of these findings are associations, not proof of cause and effect, and that many studies are small ⁴. A 2022 review from leading vaginal microbiome researchers reached a similar view: low-Lactobacillus communities are linked to higher risk of poor outcomes, but how and why is still being worked out ³.

The NHS also notes that BV in pregnancy carries a small chance of complications such as premature birth or miscarriage, although it causes no problems in most pregnancies ⁵. If you are pregnant and notice unusual discharge, speak to your GP or midwife.

How do you know what your vaginal microbiome looks like?

Symptoms only tell part of the story, partly because many changes cause no symptoms at all ⁵. The only way to see which bacteria are actually present is to test.

A vaginal microbiome test can show whether your community is Lactobacillus dominated, which species are there and how the overall balance looks. It gives you a snapshot, not a diagnosis. If you have symptoms such as unusual discharge, itching, pain or bleeding, see a GP, pharmacist or sexual health clinic first.

What can you do next?

Most of what helps the vaginal microbiome is about doing less. The NHS recommends washing the outside of the vagina with plain water and unperfumed soap, and avoiding douches, vaginal deodorants and perfumed washes ⁵.

If you would like to understand your own balance rather than guess from symptoms, our Vaginal Microbiome Test maps which bacteria are present. For practical steps, start with our complete guide.

→ How to Support a Healthy Vaginal Microbiome: The Complete Guide
→ 6 Signs of an Imbalanced Vaginal Microbiome (and What They Mean)