Our Busy MicroWorld Throughout the Life Cycle

How is our vaginal microbiome dynamically affected by the menstrual and life cycles?

Once upon a time… Vaginal life

For the bacteria in your womb and around, life is like frolicking in the waves at the beach. It can be fun, but also risky. At one moment, the bacteria may be riding a wave of prosperity and joy, but soon they are dragged underwater by the wild environment. And so it goes round and round, in more or less predictable, more or less chaotic episodes.

The vaginal environment is nowhere near as stable as it may seem at first glance (we introduce a very diverse mix of ingredients even to our skin, mouth and gut – nothing is stable or unchanging), it is a dynamically changeable place, affected by many internal and external factors. If you have not read my introduction to this MicroWorld series, have a look at it here. Most of these changes just train your vaginal micro-ecosystem to be more alert, but sometimes your immunity can get out of hand which results in infection or various signs and symptoms of imbalances. Even in a functional and problem-free vaginal era of (highly) relative stability, this place where the sun rarely shines goes through constant changes and acid tests.

Many of these tests are ensured by cyclical and non-cyclical hormonal changes over the entire course of our life. As I indicated in my previous article, the main chef and supervisor of the vaginal menu is oestrogen and, along with it, glycogen levels. Let me just remind you that glycogen is a glucose polymer and this form of glucose serves as a source of nutrients to many bacteria. And it is none other than the hormone oestrogen that is in charge of production and regulation of glycogen. The presence and amount of these two agents during our life and different phases of our menstrual cycle are not constant, and so we will take a brief look at the individual stages in a woman’s life and the changes in the vaginal microbiome that come with it. Every one of us is different, body and soul, and our vaginal microbiome is a reflection of that. Our goal is to find our own individual balance.

Hi Ho the dairy-O, the seeds begin to grow

Our vaginal microbiome is really born with us because all of us (including men) get it as a gift from our mothers during birth. Due to the remnants of the mother’s oestrogen (we do not produce any ourselves this early on), these gift microbes start to specialise in their new residence within the next few months. They form the dermal, oral, gut, and – in women – vaginal microbiomes (1). The vaginal fornix is colonised by bacteria within the first 24 hours and it remains colonised for the rest of our life (2). Keep in mind that nothing is sterile and hermetically isolated from its surroundings (except for a few ingenious parts of lab equipment and even there it does not always work out). The idea is to create relative equality and functional cooperation among the different organisms.

During the first few weeks after birth, the maternal oestrogen encourages the thickening of the vaginal epithelium and production of glycogen, and the feast of bacteria that produce lactic acid, thus an acidic pH, can begin. This first (bacterial) supper does not last very long, however. The maternal oestrogen is soon irreversibly metabolised, the vaginal epithelium grows thinner, glycogen levels drop, the pH rises and becomes more alkaline (3).

The forest micro-nursery

This means that the vaginal pH during our infancy is neutral to mildly alkaline as the presence of bacterial strains that produce lactic acid decreases due to a lack of glycogen. Thus the vaginal environment supports rather the growth of intestinal bacteria, such as E. coli, during this time, which become the main – albeit temporary – inhabitants. With approaching puberty, their numbers dwindle and Lactobacilli return to the lead once again (4).

The pubescent bacTerrier

During puberty, our own production of oestrogen starts to increase due to follicle maturation, our vaginal epithelium grows thicker and we produce more glycogen. This gives priority to species that ferment glycogen, and our vaginal pH begins to look “sour” again – like a proper teenager.

Puberty often brings many important life changes, including the start of sexual activity. The acidic vaginal pH of 4.0-4.5 and the specific bacterial inhabitants that survive there serve as an excellent protection from pathogens (2, 5). Pathogens, beware! The domestic bacTerrier bites!

The working age of bacteria

The onset of menstruation marks the beginning of reproductive age, the menstrual cycle gradually (ideally) becomes regular and the vaginal microbiome faces big – but periodical – changes, to which it adapts constantly.

In four out of five women, the acidic vaginal environment is dominated by Lactobacilli, but they are not the only and necessary determinant of a “healthy” acidic microbiome (remember that a healthy microbiome means something different to everyone). Bacterial culture methods also revealed the common presence of such microorganisms as Staphylococcus, Ureaplasma, Streptococcus, Mycoplasma, Enterococcus, Escherichia, Bifidobacterium, Candida and many others (2). You might notice the agents of certain diseases on this list, and it may seem scary, but we must not misinterpret the information. These bacteria and yeast can live peacefully as our tenants, and we cannot make the simple and classical distinction between “good” and “bad” bacteria. Some are perhaps kinder and others more dangerous, but the main thing is to maintain a balance in the environment and not let anyone gain the upper hand, not even the most innocent one. This would be the only state that could lead to a disease.

The composition and relative stability of our vaginal microbiome are affected by many things throughout our life. Our love life has an enormous influence – at what age we become sexually active, what protection we use, how many sexual partners we have and how often we make love, and what practices we favour. Other factors include the choice of intimate hygiene products and the frequency of use, age, genetics, medication, our physical and mental health, and even the choice of underwear.

Periodic changes in the vaginal environment occur during every menstrual cycle. The oestrogen levels fluctuate throughout the month, increasing slightly during the luteal phase, reaching the highest point during ovulation, and, on the contrary, they are at their lowest during menstruation which, together with the blood flow, causes the vaginal pH to rise, it grows more alkaline, and thus the microbiome may become more susceptible to infections. Our Terezka wrote a wonderful article on the topic of susceptibility during menstruation, and you can read it here.

A pithy paragraph about bacteria in pregnancy

During pregnancy, oestrogen – especially estriol – levels are high because the placenta contributes to its production. As a result, the vaginal environment is properly acidified and better protected. Studies show that the vaginal microbiome of pregnant women is diverse, more stable, and on average tends to be characterised by a higher presence of Lactobacilli than in women who are not pregnant (6, 7). This is why pregnant women who respect and support their body have a certain glow and can enjoy good health, including vaginal health. 


With upcoming menopause, oestrogen levels again begin to decrease and the menstrual cycles cease. The vaginal epithelium atrophies and vaginal fluid secretion and glycogen levels also decrease. The microbiome immediately responds to these changes in the vaginal environment and in most women, there is again a shift from a predominance of glycogen-fermenting bacteria (mostly Lactobacilli) to enteric and other anaerobic bacteria (from the intestine) (8). The vaginal environment is drier, more alkaline and less protected once again. 

Studies examining the use of vaginal oestrogen in hormone replacement therapy have yielded interesting results. However, the same as all external interventions, this one also carries certain risks. We should therefore support our body preventively, in a holistic way, as gently as possible, on a daily basis. We will certainly broach the topic of menopause again. Unfortunately, there are few relevant, informative and large studies on postmenopausal women, so it seems, dear women, that we will have to start experimenting ourselves. 

This series of articles might help us get a better idea about the workings of our miraculous nether regions throughout our whole life, in sickness and in health, and about how we can support them as much as possible. Even I myself learn a lot in preparation of these articles and look forward to the practical steps for our private investigation that will emerge from them.


(1) Dominguez-Bello MG, Costello EK, Contreras M, et al. Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci U S A. 2010;107(26):11971-11975. doi:10.1073/pnas.1002601107

(2) Farage MA, Miller KW, Sobel JD. Dynamics of the Vaginal Ecosystem—Hormonal Influences. Infectious Diseases: Research and Treatment. January 2010. doi:10.4137/IDRT.S3903

(3) Farage M, Maibach H. Lifetime changes in the vulva and vagina. Arch Gynecol Obstet. 2006 Jan;273(4):195-202. doi: 10.1007/s00404-005-0079-x. Epub 2005 Oct 6. PMID: 16208476

(4) Hammerschlag MR, Alpert S, Rosner I, Thurston P, Semine D, McComb D, McCormack WM. Microbiology of the vagina in children: normal and potentially pathogenic organisms. Pediatrics. 1978 Jul;62(1):57-62. PMID: 98750

(5) Huang B, Fettweis JM, Brooks JP, Jefferson KK, Buck GA. The changing landscape of the vaginal microbiome. Clin Lab Med. 2014;34(4):747-761. doi:10.1016/j.cll.2014.08.006

(6) Nunn KL, Forney LJ. Unravelling the Dynamics of the Human Vaginal Microbiome. Yale J Biol Med. 2016;89(3):331-337. Published 2016 Sep 30

(7) Saraf VS, Sheikh SA, Ahmad A, Gillevet PM, Bokhari H, Javed S. Vaginal microbiome: normalcy vs dysbiosis. Arch Microbiol. 2021 Sep;203(7):3793-3802. doi: 10.1007/s00203-021-02414-3. Epub 2021 Jun 13. PMID: 34120200

(8) Hickey RJ, Zhou X, Pierson JD, Ravel J, Forney LJ. Understanding vaginal microbiome complexity from an ecological perspective. Transl Res. 2012;160(4):267-282. doi:10.1016/j.trsl.2012.02.008

Kristýna Zezulová

Molecular & neurophysiology scientist

Kristýna has a cosmic quantity of questions in her head. However, the whole universe and its wise secrets are also found in the brain, and only through it. Through purely scientific experiments, even those that have been sewn on their knees for generations, they try to understand the body, mind, and peace around us and within us. She loves thinking in the open air and her life oscillates around balance.

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