You are a supra-organism: a walking ecosystem of trillions of microbes

Science · Published 26 October 2026 Swipe more like this →

In short: There are more living things on your skin than there are humans on Earth. This vast microbial universe isn't just hitching a ride; it is an essential biological organ. Without these trillions of tiny neighbors, your body would struggle to survive, manage your immunity, and even regulate your mood.

Humans are increasingly defined as 'supra-organisms' or 'holobionts'—entities composed of a host and its symbiotic populations. This means we are not just individuals in the traditional physiological sense; we are complex ecosystems. Our bodies host trillions of bacteria, viruses, and other microorganisms from all domains of life, including Bacteria, Archaea, and Eukarya. These microbes have co-evolved alongside humans over millions of years, providing essential 'ecosystem services' that are critical for our survival.

The sheer scale of this internal universe is staggering. The average human carries about 100 trillion bacteria. To visualize this, the bacterial population on your body is equivalent to more than 1,000 public toilet seats. Distribution varies by environment: moist and dark areas like the underarms, belly button, and between the toes can host 10 times as many bacteria as drier areas like the forearms or thighs. These 'good' bacteria act as a biological shield, occupying space and creating microenvironments that prevent harmful pathogens from taking hold.

The stakes of this symbiosis are high. Modern lifestyles can lead to 'microbial extinctions,' where the loss of indigenous microbes is linked to various diseases and epidemics. Science suggests that these microbes do more than just sit there; they actively influence and control our immunity, health, and even our psychological well-being and behavior. Because they are so integrated into our biology, over-sanitizing or killing off our natural flora can be hazardous, potentially allowing opportunistic 'bad' bacteria to move in and cause systemic problems.

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