You love your dog so much, it's only natural to let him lick you. And if it happens that he zeroes in on your lips, what's the big deal? After all, you've heard that a dog's mouth is cleaner than a human's.

Except it's not true. You've seen the things your dog eats. It's no wonder dogs have their fair share of oral bacteria, making them no better than us when it comes to the microbial situation in their mouths. So you may want to think twice before putting your face so close to your four-legged buddy.

Why do dogs lick?

You may think your dog is doing this out of love, but there are a number of reasons dogs lick their owners, other dogs and even themselves, according to the American Kennel Club.

They like the way you taste. Dogs find something yummy about your sweaty, salty skin. That unique taste is also comforting because it comes from someone they love.

They're rewarded for doing it. What did you do the last time your dog licked you? Likely you gave him attention by petting him or saying something to him, which offered positive reinforcement, encouraging him to do it again. And, as the AKC points out, licking also releases endorphins (the “feel good” hormones), which increases the benefit of doing it.

To show submission. Puppies will lick their mother's mouth as a sign of subordination. Similarly, a dog will lick another dog (or a person) that they feel is superior to them.

For medical or behavioral reasons. A dog might lick a certain spot on his body because of allergies or other medical problems. But a dog that obsessively licks himself, a person or even an item may have anxiety or a disorder that may benefit from a consultation with a behaviorist.

To lick or not to lick

dog licks the cheek of a baby Because babies' immune systems are still developing, it's a good idea to keep dogs from licking them on the face, say experts. (Photo: Christin Lola/Shutterstock)

Your dog's mouth and intestines harbor all sorts of bacteria and parasites. Some of these are zoonotic, meaning they can be transmitted to people and can cause disease, says veterinarian Ken Tudor of PetMD. Some common bacteria that can be transmitted this way include salmonella, E. coli, clostridium and campylobacter, which can be found in a dog's intestines.

Because pets lick their bottoms, these bacteria can eventually end up in a dog's mouth and then possibly be transferred to people with a lick.

If you're healthy, a few dog licks likely won't make you sick, most experts appear to agree.

“When dog saliva touches intact human skin, especially in a healthy person, it is extremely unlikely to cause any problems, as there will be very little absorption through the skin,” Dr. Leni K. Kaplan at Cornell University’s College of Veterinary Medicine told the New York Times.

But because disease-carrying saliva can be absorbed more readily through the membranes in a person's mouth, eyes and nose, Kaplan suggests it's best to avoid letting your dog lick those parts of your face. It's rare that illnesses are spread that way, but it's still a wise precaution.

After all, it's not just the bacteria you need to worry about.

Before you kiss a dog, or let a dog lick your face, “you have to think of where their nose has been,” veterinarian Clark Fobian, immediate past president of the American Veterinary Medical Association, tells WebMD. “Has it been inside a dead opossum on the side of the road, or the posterior of another dog, or in the litter box?”

Fobian points out that you shouldn't think kissing your dog on his nose or the top of his head is much safer than on the mouth. If your dog has an infection, germs can travel all over his body through scratching, he says. And because dogs are constantly licking, whatever is on their mouth typically will end up on their skin, and vice versa.

If you have a compromised immune system — for example if you're on chemotherapy or have diabetes — you should definitely avoid the up-close-and-personal doggy mouth to mouth, Dr. Shelley Rankin, associate professor of microbiology at the University of Pennsylvania School of Veterinary Medicine, tells VetStreet. The same rule applies for pregnant women, babies, the elderly and anyone (like teenagers with acne) who have open sores on their faces.

“Anywhere the skin is broken, there’s potentially a risk," Rankin says.

Playing it safe

dog turning away from a woman in park If you get near a dog's face and he turns away, he may be telling you he's stressed you're so close. (Photo: naeg/Shutterstock)

To limit your chances of pet-related microbial issues, it's smart to take common sense health measures to keep you and your dog healthy. Here are some tips from the Companion Animal Parasite Council:

  • Make sure your dog has regular heartworm, flea and tick control.
  • Have your dog checked for parasites regularly and have puppies on a deworming program.
  • Clean up immediately after your pet while on walks and in the yard.
  • Wash your hands after cleaning up after your pet.

And use caution when sticking your face in front of any dog. Not all dogs want you that close and can show their stress by leaning or looking away or licking their lips. If you don't catch and respect those signs, a dog can eventually snap at you, veterinarian Melissa Bain, assistant professor at UC Davis School of Veterinary Medicine, tells WebMD.

It’s just like trying to kiss a person who doesn’t want to be kissed. “We respect people who are like that; we should also respect dogs who are like that,” Bain says.

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.