The human microbiome is the sum total of all microorganisms (fungi, viruses, bacteria, and other microbes) that inhabit and reside on the human body. These microorganisms mostly live in places such as the skin, gut, mouth, and other body systems. The human gut microbiome, specifically, harbors trillions of organisms and plays vital functions in the following terms: Digestion and metabolism, immune system development and function, protection against pathogens production of essential vitamins and compounds Influence on mental health through the gut-brain axis.