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

When you sleep at night, you don’t produce as much saliva (spit) as when you are awake. Saliva helps protect and wash your teeth. The reduced production allows the bacteria inside your mouth to multiply overnight, causing the terrible taste and bad breath. If you sleep/breathe with your mouth open, your teeth dry even faster, worsening the effect.

This is also why you are more likely to drool when napping because your saliva production doesn’t go down as much as when you are asleep at night.