system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is possible that people have really bad breath at the morning even they've brushed their teeth before going to bed?
gpt
No matter how hard you scrub and rinse even with mouth wash some bacteria is going to live and/or sneak in, and then it's going to have eight hours to grow and multiple in an enclosed dark and moist environment. 

Also probably because your mouth is connected to your gut.