How Gross Is It to Let My Dog Give Me Kisses?

Ah, friends. They're like family but cooler. Fully customizable. Fall and one of them will be right there to pick you back up. But as great as friends can be, they also do a lot of really stupid stuff. Stuff that blows your mind. Like, sometimes it seems crazy that you even hang out with people who make such crappy decisions. Stuff that, were it to get out, would be mortifying for anyone with even a shred of self-respect. Lucky for your friends, they've got you to ask their deepest, darkest questions for them. And lucky for you, we started this column to answer those most embarrassing of queries. The scenario: We love our dogs, and our dogs love us back. Sometimes our canine pals like to show affection with a big slobbery tongue across the cheek. And sometimes that tongue might swipe across your lips or mouth.

We humans, on the other hand, show affection to each other by kissing with our mouths. We've all seen someone kiss a dog lips-to-lips, or you might be guilty of it yourself.

The issue: Dogs use their tongues to explore the world. They lick the ground. They lick other dogs. They lick their own butts. Even worse, about one in four dogs has eaten feces at least once, and around one in six are "serious stool eaters" who make a habit of it, according to the American Kennel Club. Many of those things—particularly fecal matter—can contain harmful pathogens.

On the other hand, there's a longstanding belief that despite those habits, a dog's mouth is cleaner than a human's. "That's actually a myth," says Beth Ann Ditkoff, a biology lecturer at Sarah Lawrence College and the author of Why Don't Your Eyelashes Grow? The notion seemed to originate with the observation that dogs lick their wounds to clean them, therefore their mouths must be clean. Although there are some antimicrobial compounds in saliva, the licking of wounds is more about removing dead skin and dirt to help speed healing, Ditkoff explains.

What's the worst that could happen: You could pick up a nasty parasite like Toxocara canis, which is a roundworm that can cause pneumonia or even irreversible blindness if the larva make their way to your eyes. "Dogs are the natural host for those worms, but when they get into an aberrant host like humans, they can have a more serious effect," says Kathryn Michel, a professor at the University of Pennsylvania's School of Veterinary Medicine. Some studies have shown that virtually every puppy is born carrying the parasite. (Cats also have their own version of the worm, called Toxocara cati.) If you have a cut on the area that the dog licks, it could get infected and lead to cellulitis, a skin infection that can spread and turn dangerous. "Less likely but still a risk could be contracting viruses or bacteria that causes respiratory or GI illnesses," says Kevin Hopkins, a family medicine physician at the Cleveland Clinic.

What will likely happen: Probably nothing. "I let my dog kiss me all the time," Michel says. "So do I worry about this? No." In order for you to get sick from a dog's slobber, a chain of unfortunate circumstances would have to happen. First, the dog has to be carrying a disease or bacteria or parasite in the first place. Second, you're more likely to get infected if they lick something other than healthy, unbroken skin. So an open scratch or cut on your face might allow the pathogen to bypass your skin's defenses. You're also vulnerable if the canine's tongue swipes across entry points to your body like your eyes, nose, and mouth.

Even then, your own immune system is probably strong enough to fend off the invaders. Dogs generally aren't filling emergency rooms with pet owners who received too much puppy love. "The good news is we dodge that bullet—and animals dodge that bullet—every day," Michel says. "If you've got a healthy immune system you usually don't get sick."

What you should do: Don't let dogs lick young babies, very elderly people, or anyone else with a weak immune system—like if they're undergoing chemotherapy. And you probably shouldn't intentionally let a dog lick you right on the mouth, and if they do, it might be smart to wash your face afterwards.