BAD
Why some make us sick.
Image: Men's Health
As it turns out, very few microbes can cause disease in humans (only about 1%) but some of those bad guys are also good guys…weird right? How is that possible?
Well, our bodies actually freak out whenever our immune systems come across anything not marked with a set of ID tags that say “hey, it’s just me!” This means that all of those helpful microbes in and on our bodies aren’t supposed to come in contact with our immune cells.
Now this is going to sound backwards but here me out; the microbes that are “inside of” us are actually still outside of us! Think of the inside of your mouth when it’s open. It’s actually exposed to the outside world so it can receive things like food and water. Your blood vessels, muscles and other tissues however are safely hidden below skin. Your mouth then connects to your throat to your stomach and so on until it connects to your colon.
Digestive tracts are really just super long tubes (~30 ft) that remain exposed to the outside world. Essentially, all the microbes “inside of” us are connected to the outside of our bodies and kept out of the real inside by a single layer of epithelial cells.
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Much like when you get a cut on your skin that gets infected, any tear in the thin layer of epithelial cells can let microbes into the sterile parts of the body, like the bloodstream. When a microbe invades this sacred territory and immune cells (specifically lymphocytes) can’t find the proper ID tags, they go whacky trying to kill the invader and prevent the entry of any of its buddies.
So that fever you get, all that gross snot that builds up and most other symptoms you tend to think of as sickness? Yeah, those are just your immune system running rampant, not the microbe itself.
In this way, any of the good microbes helping you out on the daily, can actually make you feel very sick just by crossing a single-cell-thick border. Fortunately, the immune response is pretty ferocious, which is why you can survive a few invasions here and there.
Very few microbes actually produce things like toxins or are capable of physically damaging your body. As of right now though, we've got some very effective antibiotics that can take care of these extra-bad guys.
For the most part, if you’re a healthy individual with a good immune system, the majority of microbes are nothing to be afraid of so I encourage you to embrace the bad with the good and to maybe put down the Purell every once in a while.