Here's another article about the microscopic ecology inside our bodies:Microbes Rule Your Health
The microbes that use us as a habitat outnumber our own cells by 1.3 to one. Many of them dwell in symbiosis with us and serve beneficial functions. Living in a state of complete sterility would not be good for most people. Jack Gilbert and Rob Knight, authors of DIRT IS GOOD, referenced in the article, explain why exposure to germs and other "impurities" in the environment strengthens our immune systems. Not only that, "Microbes in the gut talk to the brain." So it's to our advantage to encourage our "good" internal tenants to thrive and multiply, and the article mentions several ways to accomplish that goal.
This topic reminds me of Madeleine L'Engle's novel A WIND IN THE DOOR, in which Meg and her companions become submicroscopic to enter the body of her critically ill brother, Charles Wallace. There they meet the farandolae, sapient creatures dwelling in the mitochondria of Charles's cells, to whom his body is a galaxy. Meg and these infinitesimal beings, whom she helps to heal, awaken to the interdependence of all things in the universe, from minute farandolae to distant stars.
Considering our microbial inhabitants along with other creatures we harbor, such as eyelash mites (I know, squick), an alien observer might think our main purpose for existence is to provide a home for trillions of smaller life forms. If our tiny tenants had intelligence and could communicate with us, what wisdom might they impart?
Margaret L. CarterCarter's Crypt