eli5: Why do your teeth feel so gross when you first wake up even though the last thing you did before sleeping was brush your teeth?

Question

I assume it has something to do with the bacteria in your mouth thriving and replicating from the warm, moist, undisturbed environment…. But you’re not eating at night to help form plaque so I don’t get it.

In: 1710

Answer 1

In general, it’s because your mouth produces less saliva while you sleep. That slightly drier and more importantly less enzymatic environment along with a long period without any rinse (like drinking water during the day would provide) makes a very hospitable environment for bacteria to reproduce. That bacteria feeds on food particles and sugars and produces acids which can harm your tooth enamel, but also produce a strong smell (halitosis). So when you wake up, you’ve got lousy breath.