Dogs lick for many reasons, including communication and affection. If you find the licking bothersome, keep in mind that your dog is not trying to annoy you, he's simply finding a way to let you know he likes or needs something from you. Stopping licking behavior is not always easy and might require some training and patience.
Why Dogs Lick
Dogs lick for many reasons, including grooming, communication and affection. In the wild, dogs lick as a sign of submission -- pack members will lick the dominant dog or pack leader -- and puppies will lick their mothers and dominant siblings. Dogs lick humans for many of those same reasons. For example, they might lick you to share a message or to say "I need attention" or "I'm hungry or thirsty." Some dogs like the salty taste of human skin, so they might simply lick you because you taste good.
Ignore the Behavior
One of the best things you can do to stop the licking is to ignore it. For example, leaving the room, stepping away or simply moving your hand or face away so your dog can't lick it anymore. Never respond to licking by talking to your dog, petting him or giving him attention. This will reinforce the idea that licking works and you'll have a harder time breaking the habit.
Make Sure You Taste Bad
Taste deterrents are often used to stop dogs from licking objects or themselves after an injury or after surgery. Taste deterrents can be applied to your skin. These products are often sold in spray or gel form and come in flavors such as bitter apple, bitter cherry and spicy hot. Ask your veterinarian or doctor whether the product is safe to ingest and apply on the skin. If you get the OK, simply apply a small amount on the area of your skin your dog likes to lick. The unpleasant taste will discourage your dog from licking, though it might take a few tries before he gives up.
Back to Training
You can train your dog to lick on command. To do this, you need to first practice the "stop" command, asking your dog to stop the undesirable behavior. Once he understands, you can teach your dog to "kiss" on command, just as you would "down" or "give me five."