system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if we brush before bed, why do we wake up with bad breathe.

Do we miss a spot? Does the toothpaste not do a good enough job? Or is the human body just so full of bacteria that it's gonna smell no matter what?
gpt
not 100% of bacteria died and bacteria multiply fast in favorable environment... Like in your organic warm wet mouth. Normally saliva helps lower bacteria growth but your mouth usually becomes dry if you sleep with mouth open.