Your saliva (spit) provides a protective layer in your mouth to prevent bacteria from growing on the surface.

However, when you sleep at night, you produce less saliva so you don't drool or choke on your spit. Less saliva means the bacteria can spread over the surfaces of your mouth. The foul smell of morning breath is the waste emitted by the bacteria as they snack on any food remaining in your mouth.

If you leave your mouth open or breathe through your mouth at night, your mouth dries out faster and allows the bacteria to spread quicker.

Brushing your teeth and tongue helps get rid of the bacteria producing the foul smells.

There are billions of bacteria living in your mouth all the time. They're all constantly reproducing, peeing, and pooping. That waste smells bad.

During the day you are generating spit and swallowing, which helps to keep the bacteria populations down, and continually washes the waste away as it's produced, or at least before it can build up too much.

At night, you stop generating as much spit and you don't swallow. So all the bacteria can multiply and their pee and poop can also accumulate. That's what morning breath is. Bacteria colonies and their waste.

[removed]

[removed]