This..I don't allow my dogs to lick my face myself but not because it's dirty. It's because they need to learn to wait for food...and the only reason they lick your face is because of the smell of food. (not because they love you like some naive people think)
It's clean as it in it can do no harm...it doesn't do anything on our health (providing it's a healthy dog). My dogs are not allowed to lick me just because they need to be taught manners (can't really phrase it different atm).
As some other guy said here, licking is fine if you are the one allowing it. A dog should never be allowed to lick on his own.
Don't allow him to lick your face at all...you are confusing him by letting him do something only to stop him 2 inches to the left.