4 Answers

Victoria Stilwell of Animal Planet has this to say:
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.

Licking releases pleasurable endorphins which gives dogs a feeling of comfort and pleasure — like the feeling people get when they are biting their nails — it relieves stress. If your dog's licking is purely a sign of affection, one way to decrease this is to ignore the licking. Licking never gets attention. If your dog licks you, then you immediately stand up and walk into another room. You want to teach your dog that licking means the person will leave the room. When you pet your dog, if he starts to lick, the petting stops and you walk away. With repetition the licking will stop.

If a dog is chronically licking himself, it can be because he is bored, anxious, has skin problems such as allergies, or could be feeling pain either in their paws or elsewhere in their bodies. You should make sure your dog is getting enough stimulation and rule out any infections or allergies by visiting your vet. 

http://www.health-for-dogs.com/dog-licking-why-dogs-lick some info here

because licks are kisses 4 them. ur doggy luvs u