Dear Stephanie,

If you’ve ever caught a whiff of someone’s stinky morning breath, or even your own, you know it can be pretty rotten. We can trace the smell back to tiny culprits that live in our mouths. They are called microbes and they live around your gums, between your teeth, and on your tongue.

“They like to eat what you eat,” said my friend Claire Burbick, a veterinarian and microbiologist at Washington State University.

A feast for microbes

The microbes feed on leftover bits of food in your mouth. They not only help break down your food, but they also get energy from that food. As they eat, grow, and multiply, they also release some smelly gases—some of them might even remind you of rotten eggs.

illustrated cartoon gray cat, Dr. Universe, wearing a white lab coat, yellow pants, and a crimson shirt with Washington State University logoWhen microbes eat foods rich in protein, such as meat or dairy, they tend to grow and multiply pretty fast, Burbick said. They are particularly stinky. Something else that adds to the stink is leftover food. If food sits in your mouth too long, it will start to rot. The mouth can get kind of gross, but it also has a way to clean itself out.

Self-cleaning mouth

One way it does this is with saliva, or your spit. Saliva helps you swallow your food. It’s mostly made out of water and contains a few chemicals that help fight off bad bacteria.

Saliva is kind of like a built-in cleaning system. Of course, it isn’t perfect, so brushing your teeth also helps. Not to mention, your family and friends will thank you for it.

Bad breath isn’t just a people problem either, Burbick said. Cats, horses, cows, and of course dogs, also get bad breath. Whether snoring or just breathing deeply, sometimes animals and humans sleep with their mouths open. When air moves in, it can dry out the mouth and create an environment that makes the stinky bacteria go wild. They start to multiply and build up.

In the morning, you might wake up with some extra bad breath. You’ll probably want to brush your teeth again, sending those stinky microbes down the drain and leaving your breath fresh.

Fighting the smell

Bad breath is actually pretty common, Burbick said. It turns out humans have been battling bad breath for thousands of years—and they’ve come up with some creative ideas. Some researchers have found evidence that Ancient Egyptians mixed together spices and honey to create a kind of breath freshener. They also used thin twigs with frayed edges to scrub their teeth.

One of the first toothbrushes in human history was made in China. It had bristles made of hog hair and inspired the plastic toothbrushes humans use today. These days, humans also have minty toothpaste, gum, and mouthwash that can help mask morning breath—or garlic breath, or onion breath, or whatever kind of stinky breath might come your way.

Dr. Universe