It depends on the dog, and the person, the geographical context, etc. Dogs can carry parasites and also bacteria (like we do), and rabies can be transmitted by a dog’s saliva into an open cut or wound in your skin.
And of course, dogs love to lick their butts and drink from the toilet bowl. So there is the instinctive “yuck” factor.
There are several diseases that they can transfer to us including Zoonosis and we can also get gum disease causing bacteria AS WELL AS we can transfer that to them!
You should always wash your hands after playing with your dog and wash your face too if it has been licked.
If you enjoy the affection of your dog, manifested by their licks sometimes, let them do it occasionally. If you hate the idea, stay away from their tongues as dogs lick the faces of people they love like they lick the faces of dogs in their pack. It is a sign of respect and affection. Use common sense and be aware of dog’s saliva.
Then think about what humans can transmit from one to another if they kiss – hint, more stuff. Then think about what you immunize your pet for, and if he’s primarily an indoor pet, what he’s even susceptible to…the list gets very short, very fast.
So, it comes down to a personal decision. But as far as zoonotic diseases go, if your dog is well cared for, probably not a big risk.
John Oxford, professor of virology and bacteriology at the Queen Mary University in London, expanded further on just how much bacteria your dog’s muzzle and mouth can carry.
“It is not just what is carried in saliva. Dogs spend half 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.”