system
Given the following post, respond as if you're commenting on Reddit:
human
If we should use antibiotics sparingly, why is daily antiseptic mouthwash OK?

We've been hearing for a while now that overuse of antibiotics leads to proliferation of antibiotic-resistant strains.  Why doesn't the same apply to dental mouthwashes/rinses, which are recommended for daily use?

I understand that "old school" mouthwashes are not really antibiotic; that they work by making it harder for plaque to settle on tooth surfaces.  However, newer "burn-free" mouthwashes without alcohol, e.g. those that contain cetylpyridinium - does the same concern apply?
gpt
It is typically much harder to develop resistance to disinfectants applied externally. This is because disinfectants and topically applied antibiotics can be much more toxic to both the human and the bacterial target without negatively impacting the human. Things like bleach and alcohol are very toxic to microorganisms due to broad damaging effects, damaging effects that would occur in humans if we tried to use them internally. Consequently, bacteria cannot evolve total resistance since the disinfectant hits so many targets.

For internal antibiotics, we must damage only bacterial proteins or processes without damaging host proteins or processes. Thus the antibiotics used internally tend to have much more specific targets like cell wall synthesis or ribosomal function. As a result, bacteria are able to more readily evolve resistance since only one or two proteins are inhibited.

However, that is not to say externally applied antimicrobials are fine to use prolifically as we are beginning to discover bacteria resistant to triclosan, found in numerous products like soap and toothpaste. 

So the tl;dr version is that topically applied disinfectants like alcohol are able to damage numerous targets within the bacteria making resistance almost impossible. Think of it like a weed growing in a lawn. A weed can evolve to resist a pesticide that only targets the weed but allows the grass to grow but likely won't evolve resistance to napalm which would kill everything including the grass.