Whether we welcome our dog slurping on our face or recoil in disgust, we usually think of this behavior as an expression of love. And it is — dog kisses if you will. But dogs lick us for other reasons too. They gather information, groom and show respect by licking.
The reasons dogs lick are rooted in their psychology which is based on survival in the pack. Right after puppies are born the mom licks them to stimulate breathing and to clean them. Back when dogs were wolves, lower ranking members of the pack licked the male and female alphas' faces as a sign of subordination.
While it may seem that small dogs are more prone to face licking than big ones, there is no clear evidence that this is true. Chances are if you let your Weimaraner sit on your lap or hold your English Mastiff like a baby, they'll lick on your face just as much as a Chihuahua or a French Bulldog.
The most common reason our dogs lick us is that they're showing affection. The act of licking causes your dog's brain to release opiate-like endorphins into his system. Endorphins are calming and induce a general feeling of well-being. No wonder they want to keep doing it!
Lapping up information
When we want to understand something we watch, listen, and ask questions. When dogs want to understand something, they watch, listen, sniff, and taste. Our skin is a Wikipedia of information to them. They find it particularly intriguing when it's sweaty and salty.
Tongue as grooming tool
We usually think of cats licking themselves to spruce up. But dogs do it too. Their saliva contains enzymes that kill bacteria. When a dog licks himself he's getting rid of dead skin cells and dirt. While your dog doesn't exactly recognize that you're having a bad hair day, he may feel compelled to give you a bath just because he cares.
A slurp for respect
Your dog may be licking you to show that she respects your position as the alpha member of your little pack. If you have more than one dog, you'll notice that the ones who do the most licking on the other dogs are lower in the pecking order. Wolf and feral dog pups lick their mother's mouth to express subordination and to ask her to regurgitate her meal so they can scarf it up.
You taste good
Sometimes our dogs lick us just because they like how we taste. Notice how they often go straight for your mouth? A dog's sense of smell is phenomenal. If they can find someone who is over 100 miles away (and they can), they can certainly detect even the smallest remnant of the burrito you had for lunch.
How to discourage licking
Knowing that your dog's licking is his way of showing that he loves you, respects you, and thinks you're simply scrumptious may make it easier to tolerate. But if it still grosses you out there are ways to discourage it.
In a firm voice say, "no lick" and then gently but quickly move his face away from yours. Be sure to say "no lick" first, followed immediately by moving his head away. Soon you'll find that when you just say "no lick," your dog will move his head away himself.
You can also try disengaging with him when he starts to lick. Get up and move away. Do this repeatedly and consistently. You want to show him that licking means he will get no attention.
Be careful not to confuse your dog by inadvertently rewarding him for licking you. Sometimes when a dog licks us it's natural to reach out and give him a pat. Hope springs eternal in dogs. If you get up and walk out of the room 27 times but reward his licking the 28th time, he will forever remember that reward and keep trying for another.