A few years ago, a rich friend of mine asked me to come over to his palatial UWS apartment to help him organize his “prepper” room. He moved a china cabinet in the middle of foyer to reveal a hidden door, and behind it was enough guns, ammo, and gold to make the post-apocalypse look pretty sweet. (He even showed me how I could fit $100,000 worth of gold bars in my boots if I don’t mind blisters, and because I’m a good friend, I didn’t sprint out the door the second I was laced up.)

He also had an entire milk-crate worth of “Z-Packs”, the standard 5-day antibiotic regimen for fighting most minor infections. He said he uses the Azithromycin packs for just about anything. Got a cold? Z-pack. Stub your toe? Z-pack. Okay, not really, but in any case, I cautioned him that this wasn’t such a great plan, but I couldn’t easily explain how it worked. Yes, if you fail to take the whole dose, the remaining bacteria is weakened, but not killed off, then comes back more resistant. I get that, but how does it spread? You can’t exactly sneeze pneumonia into greater society.

Here’s the answer: It’s not that the specific internal infection that you are treating is going to come back stronger (though it could), it’s that your body’s skin and mucus membranes are little more than perambulating petri dishes, wiping and smearing staphylococcus on every keyboard, subway pole, and carton of soy milk that that lady before you picked up before having a change of heart.

The key thing to know is that Staph is on your body all the time, but your skin protects you from it. However, when you are treating an internal infection with antibiotics on a five-day regimen, after a long day at work you rub the back of your neck on the subway ride home. The staphylococcus from your neck, having survived a three-day trial-by-fire, escapes the antibiotic coups de gras by taking a ride on your fingertips to the warm surface of the subway pole, then someone else comes along on the same pole, scratches their face, and next thing you know, civilization has crumbled, and you’re eating the neighbor’s dog.

So, the take away is that it’s not necessarily irresponsible people failing to follow through with their regimen, it’s that the antibiotics treating the infection on your finger are also winnowing the bacteria everywhere else on your body, not just the infection point. So your finger may be as good as new, but now the staph under your thumbnail is now a hardened killer with a thousand-yard-stare, waiting for the next soft tissue to come alone.

So, yeah. Don’t use antibiotics if you don’t need to, wash your hands with soap, and try not to pick your nose, or you could end up getting carved up like a swiss cheese and bring about the end of the human race.