You probably shouldn't let your dog lick your face

Dr. Neilanjan Nandi, an assistant professor of medicine at Drexel University College of Medicine in Philadelphia, told the Times that many animals mouths have "an enormous oral microbiome of bacteria, viruses and yeast."

“There are some organisms unique to dogs that we were simply not meant to tolerate or combat," Nandi said.

Some bacteria in dog's mouths, like clostridium, E. coli, salmonella and campylobacter, can be transferred to humans and cause disease, according to Cornell University’s College of Veterinary Medicine lecturer Dr. Leni K. Kaplan.

But you don't necessarily have to stop your dog from licking you altogether.

"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," said Dr. Kaplan.

It's important to wash your hands and to avoid allowing your dog to lick you on the face, especially near your mouth, eyes, or nose, where pathogens and dog saliva can enter and cause illness, although it is rare.

John Oxford, a professor of virology at Queen Mary University of London, told The Hippocratic Post that it's the general habits of a dog that means you should stay out of each other's faces.

“It is not just what is carried in saliva,” he said. “Dogs spend half of their life with their noses in nasty corners, or hovering over dog droppings, so their muzzles are full of bacteria, viruses and germs of all sorts.”

For cat owners, there isn't as high of a risk since they do not eat feces, but they may, on rare occasions, transfer parasites and lead to infections, like cat scratch fever.

In general, owners should keep their pets up to date on vaccines, de-worm your new pets and keep them away from other animals' feces.