What Is With My Dog’s Obsessive Licking?

I have two dogs, a female Papillon and a male Yorkie. Both have great behavior. They listen, they are house trained, and there is no aggression.
That is, until the morning. I’m not a fan of dog slobber, so I often don’t let them lick very much. But a few mornings I wanted to see what would happen. When I wake up, my Papillon loves to lick my face as if to clean it! If my Yorkie comes over to lick my face, my Papillon will block him, growl, and in some case bare her teeth and nip him. After she drives him to the end of the bed or off the bed, she seems to have the need to re-lick my face!
Why do my dogs do this when it comes to licking my face (and why do they feel the need to lick my face in the morning!)