Vet Talk

Pup Lick Relations

Is it safe or hazardous for dogs to lick human faces?

Published: May 15, 2017
Yarra takes her Pup Lick role quite seriously and goes to town on Mark's face. Photo courtesy of Dr. Mark Rishniw.

I’m lying on the floor and my Labrador, Yarra, is licking my face, wagging madly. As if I’m made of cat-poop flavored ice-cream (if there was cat-poop flavored ice-cream, it would be every dog’s favorite flavor!). My wife rolls her eyes and continues to do whatever she’s doing as Yarra embraces her role as “Director of Pup Lick Relations.”

A few days later, my mother-in-law sends me a link to an article that appeared last year in the New York Times: “Should you let your dog lick your face?” I read through the article, and my hackles rise (and, I’m sure, Yarra’s would have if she could read). I can’t resist taking the bait. And off I go.

The article in question asks whether it is “safe” or “hazardous” for dogs to lick human faces. The reporter interviewed five people about the subject: a physician from Drexel University College of Medicine; a veterinarian in the community practice service at Cornell University’s Hospital for Animals; a virologist from Queen Mary University of London; a veterinarian who was the president of the American Veterinary Medical Association; and, finally, a veterinarian teaching in a veterinary technology program.

Based on these interviews, the reporter concludes that having your dog lick your face is unsafe and should be avoided. But on what evidence?

The physician rightly states that “most animals’ mouths are host to an enormous oral microbiome [a community of microorganisms] of bacteria, viruses and yeasts.” He fails to add that humans are animals and their mouths have a similarly enormous microbiome. We are all animals. These organisms are not only harmless, but many are necessary for us to remain healthy. Indeed, if we compare the number of cells in a human body to the number of micro-organisms (those bacteria, viruses and yeasts), we are equal parts microbe and human!

What about those zoonotic bacteria that the Cornell veterinarian mentions? (By the way, zoonotic simply means a disease can be transmitted from animals to people. There’s also reverse zoonosis in which humans infect animals; and then there’s zombinosis, in which humans become zombies, but that’s a story for a different day). The list that’s rattled off includes the scary clostridium, E. coli, salmonella and campylobacter. We immediately think of "C. diff," food poisoning outbreaks. But we all have our own clostridia and E. coli and the ones found in our bodies aren’t any scarier than the mall Easter bunny, and definitely less scary than clowns.

Still, could these doctors and vets be onto something? Surely, if face-licking transmitted these bacteria, then there would be some sort of evidence that people like me, who let their dogs lick their faces, would be much more likely to be sick from these bugs. But there is almost no evidence that owning a dog ― let alone letting it lick your face ― increases your risk of gastrointestinal diseases caused by E. coli or clostridium. Indeed, you are much more likely to get salmonellosis or an E. coli infection from eating spinach than from a dog lick. A recent study found that of 66 different E. coli strains isolated from humans and dogs living together, only two were found in both the dogs and the people – but neither one caused illness; the other 64 were equally split between being only found in dogs or only found in people. And the study didn’t identify who gave the bug to whom! It’s not surprising that pets and owners share some microbes, but it doesn’t mean that this inevitably leads to disease.

Another study found that dogs visiting health-care facilities were more likely to become infected with methicillin-resistant Staphylococcus aureus (called MRSA, a particularly nasty form of Staphylococcus) or Clostridium difficile, especially if they were fed treats or licked patients (not necessarily faces). This goes to show that sick people can infect dogs! But I’m not sick and my dog is only licking me. So what’s the harm?

There is one bacterium that has been associated with life-threatening or fatal infections in people. It’s a normal resident of dog and cat mouths that goes by the rather dramatic name Capnocytophaga canimorsus (canimorsus means “dog bite”). A particular subset of this bacterium causes infections, mostly after a bite. In almost all of the 480-odd cases of C. canimorsus infection ever reported, the patient had some sort of immune deficiency, and were either bitten or licked on a wound. Healthy people almost never developed infections. Given the number of bites, scratches and licks that the average veterinarian receives in a week, if this bug was a real threat, veterinarians would be dropping like flies!

What about viruses? So far, the only virus known to be transmitted from dogs to people is rabies. I’m pretty sure my Labrador doesn’t have rabies – first of all, she’s vaccinated, healthy, and STILL ALIVE (once a dog shows clinical signs of rabies, which is when they’re able to transmit the disease, they have 10 days to live). So, a dog could be infected with parvo, distemper, canine flu, parainfluenza, and I’d still be safe. None of those viruses can harm any person.

The virologist in the article in question just did a knee-jerk “ooh, yuck!” rather than identify any specific risks, or using the gifts that science gives us: data. I asked my local barista about my dog’s face licking. She also gave an enthusiastic “ooh, yuck!” In this context, whether she’s a virologist or a barista is irrelevant.

The AVMA president suggested that roundworms and hookworms could be problematic. However, a person is more likely to become infected with these by contact with feces, not tongues. And besides, my dog gets her monthly heartworm preventative that also kills these worms. So, no risk there from her saliva. I’m more likely to get a hookworm infection from walking barefoot in the park because hookworm larvae mostly get transmitted through the skin from wet soil.

So, to lick or not to lick, that is the question. On the face of it (yes, that pun was intended), there is little more risk than grossing out your friends or family by letting your dog give you kisses. If you’re immunocompromised, you might want to avoid this level of intimacy with your dog. But if your dog likes to lick you, and you enjoy the affection, I say pucker up! The Director of Pup Lick Relations awaits.

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