What is the human microbiome?


We’re not exactly alone in our bodies: there are about 100 trillion bacteria that join us on our journey in life. The complete collection of all these bacteria is called the human microbiome. The largest part of our microbiome is located in our intestines. You may have already heard your internal critters referred to as your intestinal flora. But it’s not just our gut: our mouth, head, skin and vagina all contain a rich collection of bacteria.

Human Microbiome Project

Until recently scientists did little research on the human microbiome. The influence of the microbiome on human development, physiology, immunity and food was largely unknown. In 2008 the National Institutes of Health (USA) launched the Human Microbiome Project (HMP). Their mission is to identify the human microbial communities and to analyse their role in relation to health and disease.

Starting before birth 

The human microbiome already starts before birth. Research shows that small amounts of bacteria are already present in the uterus, the placenta and in the amniotic fluid of the foetus. Though the foetus comes into contact with bacteria before birth, the most important starting population is passed on to the baby during natural birth through the mother’s birthing canal. These maternal bacterial species are useful and necessary for our health. They provide a large diversity of both benign and harmful microorganisms that sit on the skin, in the mouth and the intestines of the baby. Their presence ensures the baby can develop a strong permanent microbiome and a well-trained immune system.

Two young twin brothers

Composition of the microbiome 

The microbiome varies greatly per location. Some 400 bacterial species can be found in our digestive system, whereas the vagina “only” hosts some 300 types. Furthermore there are several factors that determine the appearance of your microbiome. Your living conditions affect the diversity of bacterial species in your body as much as genetics do. You will have a different microbiome if you live in the desert or at the seaside. Then again your microbiome is similar to that of your relatives and housemates. Your diet influences the microbiome as well.

Your personal microbiome

The proportion at which bacteria occur in and on your body differs from person to person. Each person has their own unique microbiome which is as unique as a fingerprint.


Interesting references

  • Mitchell CM, Haick A, Nkwopara E, Garcia R, Rendi M, Agnew K, Fredricks DN, Eschenbach D. Colonization of the upper genital tract by vaginal bacterial species in nonpregnant women. Am J Obstet Gynecol. 2015 May;212(5):611.e1-9. doi:10.1016/j.ajog.2014.11.043. Epub 2014 Dec 16. PubMed PMID: 25524398; PubMed Central PMCID: PMC4754962.


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