The human microbiome is composed exclusively of bacteria, making it essential for human health.

The human microbiome is not made only of bacteria; it also contains viruses, fungi, archaea, and protozoa that live on skin, in the gut, and other body sites. These diverse microbes help digest food, produce vitamins, train the immune system, and outcompete harmful organisms. Because of these functions, a balanced microbiome is essential for maintaining health. For example, Bifidobacterium in infants digests milk and supports gut immunity, showing how bacteria cooperate with other microbes. Thus, the microbiome is a mixed community, not just bacteria, and its diversity is key to human wellbeing.