Your vaginal microbiome is always changing - but why?

Periods, sex, hormones …

You might think your vaginal microbiome should stay pretty much the same - but it’s actually changing all the time.

Sex, periods, hormonal changes can all temporarily shift the environment your vaginal bacteria live in.

What happens to your microbiome during your period?

Let’s start with your period.

When oestrogen and progesterone levels fall, the lining of the uterus sheds as menstrual blood.

Menstrual blood has a higher pH than the vagina’s usual acidic environment, so it can temporarily make the vagina less acidic.

The importance?

Lactobacillus thrives in acidic conditions. Your vaginal microbiome can shift throughout the menstrual cycle too, with changes in microbial diversity and Lactobacillus abundance seen during menstruation. ^[1][2]

Once your period ends, the vaginal environment can move back towards its usual state. ^[1]

Can sex change your vaginal microbiome?

Yes, it can!!

Your vagina normally has a slightly acidic environment, which Lactobacillus helps maintain.

But what happens when semen enters the picture?

Semen is alkaline, with a commonly cited pH range of 7.2–7.8. When semen enters the vagina, it can temporarily buffer its acidity and raise vaginal pH. ^[2][3]

Sex can also introduce microorganisms from a partner’s genital microbiome which can change the vaginal microbial composition, including a decrease in Lactobacillus crispatus. ^[4]

What happens when your hormones change?

Your monthly cycle isn’t the only time hormones can affect your vaginal microbiome.

Pregnancy and menopause can bring bigger hormonal changes, which can also change the vaginal environment. During pregnancy, oestrogen levels rise, increasing glycogen in vaginal cells, helping create conditions that support Lactobacillus and lactic acid production.

As a result, the vaginal microbiome during pregnancy tends to become more Lactobacillus-dominated and less diverse, with greater stability. ^[2]

Then comes menopause.

As oestrogen levels fall, there is less glycogen available in the vaginal environment. This is associated with lower levels of Lactobacillus, a higher vaginal pH and changes in microbial community. ^[2]

These changes can also happen alongside vaginal symptoms such as dryness and discomfort.

Together, these changes show how hormonal shifts can shape the vaginal microbiome throughout life, from puberty and pregnancy to menopause.