Licking is a manner of greeting for dogs. You’ll notice tail wagging, excitement accompanying it, and sometimes lots of jumping around.
Love and Affection
In this greeting action, the associated emotion is love and affection. A biological reaction to this feeling is the release of dopamine and various endorphins that just feel good.
Are You OK With the Feelings?
Puppies might instinctively pick up on emotional aspects of your behavior. Similarly, they might do the same when they themselves are feeling sad or lowly.
May I Have Your Attention, Please?
Humans cannot ignore being licked, so it’s a convenient coincidence that something pups love doing rewards them with something else they love — attention!
All in Good Taste
Humans generally taste good to dogs. Of course, some taste better than others, especially after they’ve been working out or eating.