What Is Antibiotic Resistance, and Why Does It Matter?

Antibiotic resistance happens when bacteria evolve mechanisms to survive exposure to a drug that used to kill them or stop their growth. It's a natural evolutionary process — every time bacteria are exposed to an antibiotic, the ones that happen to have some resistance are more likely to survive and reproduce, and over time, and across huge numbers of bacteria and antibiotic exposures, resistant strains can become common enough to make a once-reliable antibiotic far less effective.

A few things speed this process up: using antibiotics when they're not needed (for viral infections, for example), not finishing a prescribed course, and heavy use of the same antibiotics in agriculture and livestock have all been identified as significant contributors by public health bodies like the CDC and WHO.

This is also the thinking behind the WHO AWaRe classification you'll see referenced on drug pages across this site — it groups antibiotics into three categories to help guide more careful prescribing:

• Access antibiotics are typically first-choice options for common infections, with a lower resistance-driving impact — think amoxicillin, nitrofurantoin.
• Watch antibiotics have a higher potential to drive resistance and are generally recommended as second-line choices — think ciprofloxacin, azithromycin.
• Reserve antibiotics are kept in reserve for serious infections resistant to other options, to protect their effectiveness for when they're truly needed.

None of this means any individual antibiotic prescription is wrong to take when a clinician prescribes it for an actual bacterial infection — it's a population-level concern, not a reason to second-guess an individual treatment. But it is part of why a clinician might choose one antibiotic over another for the same infection, and why finishing your prescribed course (rather than stopping early once you feel better) actually matters.