Your vaginal microbiome is a sophisticated ecosystem made up of bacteria, yeast, and even some viruses. Although less diverse than your gut microbiome (which is a good thing for your intimate health), there are still thousands of different types of microbes in this community, working together to support your health.
Just like your gut, this microbiome is dynamic and is shaped by the different phases of your life, including puberty, pregnancy, childbirth, and the menopause. Among all the different microbes that make up your vaginal microbiome, one group (known as a genus) truly stands out: Lactobacillus.
The critical role of Lactobacilli in the vaginal microbiome
This friendly group of bacteria can make up over 90% of the vaginal microbiome and is essential for maintaining balance for a healthy vaginal microbiome. This is because they produce lactic acid as a by-product of fermentation and help maintain a low vaginal pH (typically below pH 4.5). This acidic environment (anything below 7 on the pH scale is considered acidic) protects against infections by suppressing the growth of potentially harmful opportunistic bacteria, fungi, and viruses.
It's a give-and-take relationship between your body (the host) and these resident friendly bacteria. The complex cells that line your vagina store and release a type of long-chain carbohydrate called glycogen, which is influenced by the hormone oestrogen. Lactobacilli cannot directly break down this glycogen chain, so they get some help from a local enzyme present in your vaginal fluid, called α-amylase. This enzyme cuts the glycogen chain into simple sugars, for the Lactobacilli to metabolise, which as a result, produce lactic acid.
As mentioned above, this lactic acid lowers the pH of your vagina, making it acidic, inhibiting the growth of potentially harmful microbes. Some Lactobacillus species also produce hydrogen peroxide, which has been shown in laboratory settings to kill harmful microbes including Gardnerella vaginalis, Neisseria gonohorreae, and Candida albicans.
Hormones: our body’s chemical messengers
Hormones like oestrogen and progesterone regulate numerous bodily functions, including the menstrual cycle, pregnancy, and the menopause. These hormones also have a significant impact on the composition and stability of the vaginal microbiome.
Because oestrogen plays such a vital role in regulating the glycogen fuel needed for Lactobacillus to thrive and dominate, it’s important to understand exactly how hormonal changes (which may affect oestrogen levels in the body) can influence the composition of the vaginal microbiome throughout different life stages.
1. Puberty
During puberty, rising oestrogen levels trigger an increase in glycogen production in vaginal cells. Glycogen acts as a food source for Lactobacilli, encouraging their growth. This marks the beginning of a more stable, Lactobacillus-dominant microbiome, which helps protect against infections and supports reproductive health.
2. Menstrual Cycle
Throughout the menstrual cycle, hormone levels fluctuate:
● Follicular phase (before ovulation): Oestrogen rises, encouraging a more acidic and Lactobacillus-rich environment.
● Luteal phase (after ovulation): Progesterone dominates, and some studies suggest this might make the microbiome slightly more diverse and in turn is associated with a higher risk of thrush during this stage.
● Menstruation: Blood can temporarily raise vaginal pH, potentially reducing Lactobacilli and allowing other microbes to flourish. This explains why women have a higher risk of Bacterial Vaginosis during this stage. The good news is this heightened risk is usually temporary, and the microbiome typically rebalances quickly after menstruation has finished.
3. Pregnancy
Pregnancy brings a dramatic surge in oestrogen and progesterone. Interestingly, during pregnancy, the vaginal microbiome often becomes even more dominated by Lactobacillus species, providing enhanced protection to both the mother and the developing baby. This microbial stability is thought to be nature’s way of minimising infection risks during such a crucial time.
4. Menopause
With menopause comes a significant drop in oestrogen. This leads to:
● Reduced glycogen levels
● Decreased Lactobacilli
● Higher vaginal pH
As a result, the vaginal microbiome may become less stable and more susceptible to infections, dryness, and irritation—a condition known as Genitourinary Syndrome of Menopause (GSM). This also explains why post-menopausal women are more susceptible to bacterial vaginosis, thrush and urinary tract infections.
Supporting a healthy vaginal microbiome
Here are some science-backed tips to maintain a healthy balance:
● Research suggests those with higher plant nutrient (phytochemicals) intakes tend to have a more balanced vaginal microbiome. To support general vaginal health, aim for 5 servings of vegetables, 3 servings of wholegrains, 2 servings of fruit, and 1-2 servings legumes, nuts and seeds per day.
● Avoid douching or using harsh or perfumed soaps as this can affect the vagina’s natural pH levels
● Wear breathable, cotton underwear (and avoid strong detergents)
● Maintain good hygiene during menstruation, as sanitary pads and incontinence liners can often contribute to microbial imbalance
● Consider a live bacterial supplement using scientifically-proven bacterial strains (such as Lactobacillus acidophilus La-14® and Lactobacillus rhamnosus HN001™), if you notice any changes in your vaginal microbiome
● Talk to your healthcare provider about hormonal treatments if needed. Treatments such as vaginal oestrogen are safe and effective for the majority of women, and can be used alone or alongside systemic hormone replacement therapy
The relationship between your hormones and your vaginal microbiome is a dynamic one that impacts many aspects of vaginal and overall health. By understanding how your hormones influence your microbiome, you can make informed choices to support your intimate health through every stage of life.
Find out more about how to care for your vaginal microbiome here
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Written by Rachel Redman - Registered Dietitian
Reviewed by Dr. Fionnuala Barton - GP & British Menopause Society accredited Menopause Specialist
