The Debunker: Is a Dog’s Mouth Really Cleaner Than Yours?

by Ken Jennings

Dog lovers: could there be a better month than August to salute our canine companions? After all, August 10 is the day poor Rin Tin Tin died, and it’s the day Snoopy celebrates his birthday, in a 1968 Peanuts strip. Two weeks later, on August 26, it’s National Dog Day, according to the Animal Miracle Foundation & Network. To celebrate the dog days of summer, we’ve unleashed Jeopardy!’s Ken Jennings, who will correct some of man’s worst misconceptions about man’s best friend.


The Debunker: Is a Dog’s Mouth Really Cleaner Than Yours?

You’ve probably heard the old saw about the counterintuitive cleanliness of a dog’s mouth. It often gets trotted out by embarrassed pet lovers when they catch the look of disgust in your eye as their Irish setter’s tongue has its way with their hands/face/tonsils. Sure, sure, this is a mouth that spends all day grubbing around in dirt, feces, its own genitals, other dogs’ butts, etc., but somehow it’s so clean you can eat off of it. Right.


This misconception may have its roots in the well-known facts that dogs rarely suffer from tooth decay, or that dogs will lick their own wounds to clean them. Those are both true, but they have nothing to do with bacteria counts. Your doggie’s lack of cavities mostly has to do with his diet (less sugary than yours), the shape of his teeth (pointier than yours), and his lifespan (shorter than yours). And dogs don’t lick their wounds because their saliva is sterile. It’s the licking action itself—the abrasion of the tongue—that cleans out dead cells and dirt. Dogs are descended from wild canines that didn’t have access to sinks and Bactine.

The bacterial count in a dog’s mouth, I’m afraid, is roughly the same as yours: off the charts. Billions of microbes, of hundreds of different varieties. But! Here’s the good news: plenty of the bugs in a dog’s mouth will do you no harm, no matter how much you French-kiss Fido. That’s because they’re species-specific. You can’t give him your version of staph and strep, and he can’t give you his. But there are diseases that are communicable between species by saliva, including biggies like rabies. So if you regularly wind up covered in doggy drool, it’s not a bad idea to have some hand sanitizer on hand.

Quick Quiz: Speaking of canine mouths: what’s the name for a woolen Scottish fabric with a pattern of small broken checks?

Ken Jennings is the author of six books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at or on Twitter as @KenJennings.