What Causes Morning Breath?

Some mornings, the only thing that can convince you to get out of a warm, snuggly bed is the overwhelming stench emanating from your own mouth. Possibly the only thing worse than morning breath is the alarm clock itself, but no amount of brushing, flossing, or stinging mouthwash rinsing the night before seem capable of saving you from the stinking scourge. What gives?

Here’s the good news: Morning breath is just regular, run-of-the-mill bad breath, or halitosis—a diagnosis that sounds much worse than it is. While chronic halitosis is fairly uncommon, most people wake up with some form of oral unpleasantness, and there’s nothing medically worrying about it. But that doesn’t make it any more of a joy, especially for the first person you talk to before brushing your teeth.

The key to understanding why our breath smells first thing in the morning is to first understand why it doesn’t smell the rest of the time. As we go about our usual daylight business, bacteria are at work breaking down all the amino acids, proteins, and other chemicals left behind in our mouths from our last meal. This process produces volatile sulfur compounds (VSCs) like hydrogen sulfide, dimethyl sulfide, and methyl mercapatan, which are responsible for the funk. In our waking hours, our own saliva washes away the bacteria before they can do their smelly damage; when we fall asleep, our saliva production calls it a night, too.  In the absence of much saliva, the VSC-causing bacteria run wild, and the sulfuric compounds build up until their grand unveiling in the morning.

It’s a simple equation—mouth plus bacteria minus saliva equals yuck—but the bad news is that there’s not much we can do about it. Brushing before bed will help minimize the damage by reducing the amount of compounds for the bacteria to feed on, and drinking a glass of water before bed will compensate at least a little bit for the impending loss of saliva.  Other than that, keep your mouth locked down in the morning until you can get to a toothbrush, and we’ll all live happier, fresher-smelling lives.