system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my mouth taste so fucking awful when I wake up?

Even if I brush my teeth just before I go to bed, why does it taste so horrible when I wake up?
gpt
Brushing only removes the build up of plaque, food, etc on your teeth/gums/tongue. The bacteria is there regardless. When you sleep, breathing and reduced saliva production increase the levels of bacteria in your mouth. These bacteria aren't harmful, they just leave their waste in your mouth and that's what tastes so bad.