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

The bacteria had time to multiply and grow, but the biggest reason is that your mouth dries out while you sleep (especially if you breathe through your mouth at night, as you probably do if e.g. you’re overweight). That drying concentrates the sugars and proteins dissolved in your saliva into a thick, sticky film that (a) feels and tastes kinda gross and (b) is a lovely place for bacteria to hide out.