What Is the Microbiome and How Does It Affect Health?

The human microbiome — the vast community of microorganisms living in and on the human body — has emerged as one of the most exciting and rapidly advancing areas in biomedical science. Decades of research have revealed that these trillions of microbial inhabitants are not passive residents but active participants in our health, influencing everything from immune function and metabolism to brain chemistry and mental health. Understanding the microbiome is increasingly essential for understanding human biology.

What Is The Microbiome?

The human microbiome comprises all the microorganisms — bacteria, viruses (the virome), fungi, archaea, and protozoa — that live in and on the human body. The vast majority reside in the gastrointestinal tract, particularly the large intestine.

Scale: The human gut contains approximately 38 trillion bacteria, roughly equal to the number of human cells in the body. These bacteria collectively encode more than 100 times more unique genes than the human genome — a genetic repertoire called the metagenome that provides metabolic capabilities our own cells lack.