This system of bacteria, fungi, viruses, and protozoa living on your skin and in your mouth, nose, throat, lungs, gut, and urogenital tract is referred to as the "human microbiome."

It varies from person to person based on factors such as diet, health history, geographic location, and even ancestry. When your microbiome falls out of balance, you can become ill.

Those organisms perform a multitude of functions in key biological systems, from supplying critical vitamins to fighting pathogens, modulating weight, and metabolism.

This army of organisms also makes up 70 percent of your immune system, "talking" directly to your body's natural killer T-cells so that they can tell apart "friendly" microbes from dangerous invader.

Meanwhile, it's becoming common knowledge that growing up in an overly clean environment – complete with antibacterial soap and hand sanitizers – might backfire because it keeps you from getting normal and healthy microbe exposure.