Not so long ago, most people thought that the only good microbe was a dead microbe.
But then scientists started to realize that even though some bugs can make us sick and even kill us, most don't.
In fact, in the past decade attitudes about the bacteria, fungi, viruses and other microbes living all over our bodies has almost completely turned around. Now scientists say that not only are those microbes often not harmful, we can't live without them.
"The vast majority of them are beneficial and actually essential to health," says Lita Proctor, program director for the Human Microbiome Project at the National Institutes of Health. The project is identifying microbes on key body parts, including the nose, gut, mouth, and skin, in order to get a better sense of the microbes' role in human health.