yorkie opening its mouth

“A dog’s mouth is cleaner than a human’s” is a common myth that few people explore further to see if it is an actual fact. But how do dogs’ mouths compare to cats’ mouths? Do dogs really have the cleanest mouths?

Dogs’ mouths contain about 600-odd types of bacteria—80% of which are not found in human mouths. Comparatively, cats’ mouths have about 200 different bacteria and share about 50% of their mouths’ microbiomes with dogs. So, dogs’ mouths are actually dirtier than cats’ if bacteria numbers are the only things being considered.

Dogs’ Mouths: How Much Bacteria Is in There? Compared to Humans? Compared to Cats?

It’s almost impossible to compare a dog’s mouth to a human’s mouth. According to Floy Dewhirst, a bacterial geneticist and Harvard professor, humans and dogs only have about a 15% crossover in their mouths’ microbiomes. This means that only 15% of the bacteria in a dog’s mouth can be found in a human’s mouth.

Dogs and humans both have about 600 different types of bacteria living in their mouths. This doesn’t mean that dogs’ mouths are cleaner than humans. It just means that their mouth microbiomes are different.

While we certainly don’t consider a microbiome of 600 bacteria clean, it’s important to remember that not all bacteria are harmful. Some of the bacteria found in both dogs’ and humans’ mouths are necessary and helpful for digestion, which starts in the mouth!

Comparing a dog’s mouth to a cat’s is a little more concise in cleanliness. Cats are notoriously clean animals that have an incredible ability to keep themselves clean using—you guessed it—their mouths! A cat’s mouth ecosystem contains about 200 different types of bacteria, about 50% of which can also be found in a dog’s mouth.

This crossover means that cats’ and dogs’ mouths can be more easily compared to dogs’ and humans’ mouths. If you’re looking solely at the biodiversity of a mouth and judging its cleanliness based on that information, then yes, a cat’s mouth is cleaner than a dog’s. But if we left the answer there, we’d be doing you a disservice.

close up of a german shepherd on a leash with mouth open
Image courtesy of Pixabay

What Does It Mean for an Animal’s Mouth to Be Clean?

Bacteria are essential to life. Your stomach and body are filled with bacteria necessary for your continued survival. You may have heard the term “good bacteria” used to differentiate between bacteria that are helpful to you and pathogens that make you sick.

The truth is that most of the bacteria found inside your body, especially those inside the mouth and digestive tract, are significant to digestion. The bacteria found in your mouth, esophagus, stomach, and digestive tract are used to break down food into essential nutrients that you use to power your body’s functions.

Therefore, it’s not really accurate to say that a dog’s mouth is “unclean” because it has a lot of bacteria. Similarly, it wouldn’t be correct to say that a cat’s mouth is “cleaner” because it’s less biodiverse.

Everyone’s mouths are filled with bacteria. It doesn’t matter if you brush your teeth twice an hour; your mouth will still be filled with bacteria. If it weren’t, you wouldn’t be able to eat again. Wouldn’t that be terrible?

However, there is a distinction between the helpful bacteria that call your mouth home and the harmful pathogen that makes you sick. Studies have found that dogs’ mouths are less likely to pick up and house harmful bacteria than humans’ mouths. Some might say this makes their mouths cleaner since humans are more likely to pick up an oral pathogen than dogs, but that’s just an opinion rather than a scientific fact.

Can I Kiss My Dog on the Mouth?

If the question you’re asking was more along the lines of “is it safe to kiss my dog on the mouth?” we’re pleased to inform you that, scientifically, it is safe to kiss your animal on the mouth, with one catch. Your mouth must be healthy for it to be safe for both parties. Some diseases can be passed from humans to pets, and vice versa, like influenza, between ferrets and their humans.

So long as your mouth is clean and not infested with pathogens, you should be fine to kiss a healthy animal, even on the mouth.

Final Thoughts

While the idea that a dog’s mouth is cleaner than a human’s mouth probably isn’t going away anytime soon, having all the facts can help you make good decisions when you want to show affection to your dog. While a dog’s mouth may not be cleaner than a human’s, kissing your dog’s mouth is a relatively benign behavior that endangers no one.

Featured Image Credit: Pixabay