A famous guy once noted that there are more micro-organisms living on or in the human body than there are cells. This fact might make your skin crawl. Actually, the skin crawling could just be the mites living in your pores…

The fact is most microbes that inhabit your body won’t cause you any harm at all–they help your body to work and will only harm you if the environment that is you gets messed around.

Let’s talk about your mouth. Right now, there’s a ton of bacterial species living in there. Dental plaque, for instance, is actually a cool thing called a biofilm (read: layers upon layers of microbes living on a surface). These microbes form a neat little community, where the outer layers protect the inner layers from the environment. Biofilms are less cool when they show up in other places, like on transplant organs or your Grandmother’s hip replacement. But who could blame them? That shiny metal non-airport friendly attachment to Granny’s pelvis just looks like such a nice place to hang out.

Many kinds of microbes live in your gut too. In fact up to half of the mass of one’s excretions (of the number two variety) are made up of bacteria. The gastrointestinal tract, including the colon, is home to quite an ecosystem. Microbes benefit our digestion and we provide them with warm, quite acidic shelter. Our gut also plays a role in developing the immune system such that we don’t become allergic to anything and everything. This works because the bacteria essentially train the immune system in early childhood to not react to harmless antigens. Antigens–typically toxic or infectious–are like little invading troops in your body. In this extended metaphor, gut bacteria are like the mean drill sergeants making your immune system do pushups in the mud because someone sneezed near you. Unfortunately some of you drew the bacterial short straw and got the microbe equivalent of the housemate who never take out the rubbish or pays rent on time.

If you’re feeling squeamish, don’t worry. They won’t hurt you, for the most part. Your little guys just want a warm home and something to eat, and in exchange they are helping your digestion and keeping you healthy. It’s actually a pretty good deal.