What Antibiotics Do (and Don't)

Antibiotics kill bacteria, and only bacteria. They do nothing to viruses, which is why they can't cure a cold or the flu. Here's why: antibiotics work by attacking machinery that bacteria have but our cells don't, like the bacterial cell wall or their specific protein factories. Viruses have none of that; they're barely-alive packets of genetic code that hijack your own cells, so there's no bacterial target to hit. Taking antibiotics for a viral infection is worse than useless. It doesn't help you, and it breeds resistance: any bacteria that happen to survive the drug pass on their resistance, so the antibiotic works less well next time, for everyone. That's why finishing a prescribed course and not demanding antibiotics for every sniffle actually matters at a population level.