The human body hosts trillions of microorganisms—bacteria, viruses, fungi, and other microbes—collectively called the microbiome. These tiny inhabitants aren't just passengers; they're essential partners in human health.
Your gut alone contains roughly 100 trillion bacteria, weighing 2-6 pounds. These microbes digest certain foods, produce vitamins, train the immune system, and even influence brain chemistry. The gut microbiome is sometimes called a "forgotten organ."
Each person's microbiome is unique, shaped by birth method, diet, medications, environment, and genetics. You're more likely to share microbiome species with your family and housemates than with strangers—microbial communities spread through close contact.