You’ve probably heard the expression “a dog’s mouth is cleaner than a human’s mouth” at least once in your life. Most of us have just accepted this as fact, when we think about it at all, but have you ever wondered if it is actually true?
Here’s a hint: the answer is no.
Apples and Oranges
Comparing a dog’s mouth to a human’s mouth is “like comparing apples and oranges,” according to Colin Harvey, a professor at the University of Pennsylvania’s School of Veterinary Medicine and the executive secretary at the American Veterinary Dental College.
This is because both dog and human mouths are full of microbes. While there is some overlap in the types of bacteria between species, there are also a host of different dental bacteria in your dog’s mouth that you won’t find in yours.
Dogs have more than 600 different types of bacteria in their mouths, which is a similar number to the 615 and counting types of bacteria Harvard researchers have found in human mouths. These bacteria can also be joined by other bacteria that we (humans and dogs) pick up from our environments, adding to the mix.
Can Humans Get Dog Germs?
Most of the bacteria in your dog’s mouth are not zoonotic, which means you probably won’t get a disease from a big old doggy kiss. There are exceptions to this. Dogs that are fed a raw diet are at an increased risk of contracting salmonella, which can be spread to humans, and you really don’t want to share kisses with a dog that regularly raids the litter box.
In other words, kissing your dog is less risky than kissing another human, but that does not mean that your dog’s mouth is necessarily cleaner than a human’s — he just has a mostly incompatible set of germs.
Can Dog Saliva Heal Wounds?
While we’re on the subject of dog mouths, there is another folk belief that you’ve probably heard before about dog mouths: dog saliva helps heal wounds.
This gets a little more complicated. Most mammals, humans included, lick their wounds. Historically, ancient cultures even believed that dog saliva had curative powers, and the Greeks and Egyptians both used dog saliva in healing practices and featured dogs in their religious healing rites.
They may have been on to something. The act of licking, alone, offers some benefits to wound healing. The tongue removes dirt and debris from the wound site, which lowers the risk of contamination and infection.
But what about the saliva itself?
As it turns out, there are certain proteins in saliva called histatins that can ward off infection, and further research has revealed that there are other beneficial chemical compounds in saliva that can help protect cuts from bacterial infections. As if that wasn’t enough, there is even more evidence that suggests licked wounds heal twice as fast as unlicked wounds.
Does this mean that you should have your dog lick your wounds, or that you should lick your own wounds?
Probably not. Not all of the research about saliva was good. Curative properties aside, saliva has its risks. Take the bacterium Pastuerella, for example. This bacterium is harmless in the mouth, but can lead to serious infections if introduced into an open wound, resulting in sickness, amputation, and even death. And there are plenty of other germs we can pick up from our environments in our mouths that we do not want a wound exposed to.