Why is the dog licking ?
Right from birth that is how the mother communicates with her new puppies, how she stimulates them to start breathing and how she cleans them when they are born, so it’s very important to the survival of puppies. In the wild and in domestic dogs, you’ll find they will lick around the mother’s mouth as newborns and puppies still retain that instinct. It’s also sort of a submissive gesture — the more subordinate members of a pack will lick the more dominant members and that’s important in maintaining pack harmony.
Dogs also lick because they like the taste of an owner’s salty skin and out of habit. Mostly, with domestic dogs, it’s a sign of affection.