We’ve all heard the adage that a dog’s mouth is cleaner than ours, but where does this statement come from? More importantly, is it true? The American Kennel Club has weighed in on whether dogs have cleaner mouths than humans, and the most concise answer is “no, dogs’ mouths are not cleaner than humans’.”1
However, it’s not a simple yes or no question. Comparing a dog’s mouth to a human’s is like comparing apples and oranges. They aren’t biologically or chemically similar enough to make the comparison.
Differences Between Dog Mouths and Human Mouths
Our mouths are what we call “microbiomes,” or places where microbial organisms like bacteria thrive and grow. All animals have a mix of good and bad bacteria in their mouths; not all bacteria are classified as a “pathogen,” something that makes you sick. Humans have about 615 different microbes in their mouths at any given time, and many of these microbes are not present in dog mouths and vice versa.
This goes for both pathogens and beneficial bacteria. For instance, the bacterial family Porphyromonas is known for causing periodontal disease in humans and dogs. However, the strain of Porphyromonas found in humans is Porphyromonas gingivalis, while dogs usually get Porphyromonas gulae. While both germs would be considered pathogens to their respective hosts, these bacteria are not natively found in both species’ mouths. Unless your dog has been licking inside your mouth, it’s unlikely we’ll discover Porphyromonas gulae in your mouth. But that doesn’t mean your mouth is cleaner than your dog’s; you might still have Porphyromonas gingivalis in your mouth!
Can Humans and Dogs Swap Pathogens?
Some pathogens are transmissible between human and animal companions. For instance, ferrets can get the flu from humans, and influenza can be dangerous. However, most bacteria and viruses in your mouth can’t be “given” to your dog and vice versa. Assuming your immune system is functioning correctly, your immune system will kill off any bacteria or viruses passed from your dog to you.
To begin with, most of the bacteria that infect dogs can’t infect humans. However, there are some notable exceptions. Both humans and dogs can contract salmonella. It’s more common for dogs who get fed a raw diet to contract salmonella, and this disease can be spread between humans and dogs.
Dogs are also known for eating things that most humans would consider immoral to even touch, like cat feces. So, the number of external pathogens introduced to a dog’s mouth microbiome is much higher than humans. From a young age, we teach our children not to put things in their mouths to avoid introducing bacteria to their systems. Dogs don’t care about that wisdom!
So, sharing a mouthy kiss with your dog is probably best avoided. While it’s okay to let your dog lick your fingers and hands, you should try to avoid letting your dog lick your face. If you’re determined to get face kisses from your dog, remember to wash your face after to reduce the risk of catching something from your dog.
The myth that a dog’s mouth is cleaner than a human’s mouth may originate from the fact that you can’t catch most of the illnesses that dogs’ mouths are full of. There’s no end to the number of pathogens you might see from kissing a fellow human, but only a few you might get from your dog. Looking at it like that, it might genuinely seem that a dog’s mouth is cleaner than a human’s mouth. But the actual reason behind that is that dogs and humans have incompatible mouth germs.
Can Dog Saliva Heal Wounds?
When cats or dogs get injured, we often see them licking their wounds. This led the ancient Greeks to believe that dog saliva had a magical healing property. Indeed, they would use dog saliva in many of their herbal medicines for wounds, and dogs were featured in religious healing ceremonies. This history may have influenced the perception that dogs’ mouths are cleaner than humans.
The truth is that most mammals, humans included, are known to lick their wounds. We’ve all experienced that strong, primal urge to put our finger in our mouth after getting a paper cut. This primal urge extends back into the hunter-gatherer phase of humanity. When we lick a wound, the tongue removes dirt and debris from the damage, lowering the risk of infection of the wound. However, licking too much could worsen the injury or even create new injuries to the skin, such as in dogs who suffer from hot spots.
They may have been onto something regarding a healing property, though. We’ve found that saliva contains proteins called histatins that help protect the body against infection. Further research indicates that other beneficial compounds in saliva can protect cuts from bacterial infections and that licked wounds heal twice as fast as unlicked wounds.
Now, this doesn’t mean you should start having your dog lick your wounds or that you should lick your wounds. Though saliva has unique healing property, it also presents special risks not present in more conventional medical methods. Your saliva is still part of your mouth’s microbiome, and it contains more than just beneficial proteins and compounds. It also includes pathogens. Pasteurella bacteria are harmless when in the mouth, but if introduced to a wound can cause infections severe enough to warrant amputation or even cause death.
So, unfortunately, dogs don’t have cleaner mouths than humans. But, since you can’t catch most of the pathogens in their mouth, you don’t have to worry too much if a dog wants to give you a kiss. Their saliva does have some healing properties, too, which is pretty cool of Mother Nature!
Related Read: How Clean Is a Cat’s Mouth Relative to Dogs and Humans?