It's something that happens only in movies—the wakeup kiss. Looks awesome on the big screen, but in real life, there's something else to contend with: morning breath.

That sour, stale dragon breath is why most of us make an effort not to breathe too close to anyone before brushing our teeth in the morning. But why is morning breath so stinky? Sure, you’ve just gone eight hours without brushing your teeth, but you do that plenty of times during your waking hours, too.

A lot of it comes down to lack of saliva production while you're sleeping, says Mazen Natour, D.M.D., a Manhattan-based prosthodontist. Saliva normally clears out odor-causing bacteria. So overnight, when we’re not producing enough of it, the smelly bugs can multiply.

So, the drier your mouth, the higher your chances of getting nasty morning breath. Breathing through your mouth, snoring, and using certain medications can also contribute to dryness, which can make morning breath even worse (Here are 5 products that will cure your bad breath).

In most cases, morning breath is nothing to worry about. But in some situations, unusually bad breath could indicate an underlying health problem. It’s often the first sign of gum disease, which is linked to heart disease and strokes. Other times, it indicates an infection like an abscess or a gastrointestinal problem like GERD, says Dr. Natour. Talk to your doctor if your breath is suddenly stinking more than usual.

If you want to make your breath more tolerable in the morning, make sure to brush and floss carefully right before bed, since leftover food particles provide more food for bacteria to multiply in your mouth overnight.