I. What does it mean when a dog licks its lips?

If you try to force a dog to lie flat on the floor in a submissive position, after the dog eventually stops struggling and relaxes, most will flick their tongue as if they were licking their lips or the air. While most dog owners tend to view their pets' various licking behaviors as signs of love, in this case, the dog's behavior has a completely different meaning. Some new research suggests that when a dog is stressed, perhaps sensing a negative emotional state in another dog, it may trigger this non-social contact form of lip-licking behavior.

Settling behavior included in puppy behavior
Over the past few decades, researchers have begun to recognize that dog licking behavior can convey information about dominance, intentions, and mental states. The current consensus is that lip-licking or air-licking is primarily a settling behavior. The one thing that all settling signals have in common is that they contain elements of puppy behavior in them. Puppy behavior is the equivalent of a "white flag" because most adult dogs tend to raise their own species' offspring and seem to have a strong disincentive to attack puppies. As a result, non-dominant, fearful or weak adult dogs will adopt puppy-like postures and adopt puppy behaviors to avoid the attack. These behaviors usually soften the threatening person and usually avoid the physical attack. Many aspects of settling behavior involve the action of licking.

As puppies slowly grow in the litter, they begin to lick themselves and their companions clean. This mutual licking and grooming behavior serves several social functions. It helps keep the puppies clean, but in the process, it helps strengthen the bond between the puppies. The actual mechanism for building this bond is mutual gratification. Puppies can go through their companions to get to those hard-to-reach places like ears, backs, and faces, and they can return the favor by licking the same places their companions do. Because friends and family cultivate this behavior as a thoughtful gesture, the very act of licking another dog takes on meaning as a form of communication. Licking thus shifts from a practical act to a ritualized gesture. At this time in a puppy's life, the gesture means kindness and acceptance. Every puppy is saying, "Look how friendly I am. As the puppy matures, the message from the lick remains friendly, but also expands to include "I'm not a threat" and perhaps the submissive plea, "Please accept me and treat me well."

Licking to request food and show respect
Licking can take on another meaning later in a puppy's life, usually when they become less dependent on breast milk. In the wild, when a mother wolf returns from a hunt, she has fed herself with her prey. When she enters the den, the pups gather around her and start licking her face. To a human, this looks like a loving greeting, and all the puppies are ecstatic about their mother's return after being away for several hours, and could easily be seen as kissing her with happiness and excitement. However, these face-licking actions are more practical. Wild canines have well-developed stomach reflexes, and puppies lick their mother's face and lips to get her to spit out some of her food. It is easier for the mother to keep the food in her stomach than to drag something back to the litter with her in her mouth. In addition, this partially digested material is an ideal food for puppies. However, this puppy-induced gastric reflex is not common in domestic dogs unless the puppy is not well fed.

Understanding the development of licking behavior helps explain some of the other situations in which it occurs. Adult canines licking their faces may be a sign of respect or deference to a more dominant dog. Dogs that lick usually lower their bodies to make themselves smaller and then raise their heads, which adds to the posture of puppy behavior. The dog receiving the face lick shows his dominance by standing up and accepting the gesture, but not licking the other dog in return.

Nervous licking is like lip-biting in humans due to nervousness
It is often a nervous and fearful dog who exhibits licking behaviors that have become so ritualized that even when there is no dog or person close enough to lick, an anxious dog may lick his lips, just as a nervous person may bite his lips. Sometimes a dog will quickly stick out its tongue and look like it is licking the air. At other times, the dog may lie down on the floor and nervously lick its paws or body.

I often see this lip-licking or air-licking behavior when I come to the house to train a dog. These dogs are often nervous because their owners are a little nervous and the dogs are nervous because they see a strange and strong dog trainer. However, the licking behavior quickly disappears as the session progresses. Many vets often observe the same behavior in their offices. This dog was licking the air and lips precisely because he was anxious and troubled by this new environment full of strangers and unknown events.

Experiments prove dogs are more anxious about people
Some new research suggests that this licking behavior in dogs can be triggered simply by observing negative emotions in other dogs or people. The research team was led by Natalia Albuquerque of the School of Life Sciences at the University of Lincoln in the United Kingdom. The dogs used in this study were different breeds of pet dogs. The researchers showed the dogs photos of unfamiliar people or dogs' faces that showed different types of emotions (in this case, happy or mischievous faces, rather than angry or belligerent faces). The photos were displayed side-by-side, and the scientists videotaped the dogs looking at the photos and their reactions.

The results showed that when dogs were shown a dog or a human face that showed an angry or aggressive expression, about one in five times it triggered the dog to lick its lips or lick the air. The researchers interpreted this as a sign that seeing such a negative emotional image would produce a brief, low-level stress response in the dog. This mild stress or anxiety was enough to trigger the dog to lick involuntarily and quickly. They conclude that this confirms that this licking behavior represents worried anxiety in the dog.

There was an interesting situation in these tests. Dogs were twice as likely to lick their lips or lick the air when confronted with a negative facial expression from a human than when confronted with a negative expression from another dog. This is a puzzling finding for which the researchers have no clear explanation. However, one speculative possibility is that humans are much more responsive to facial expressions than dogs. If this is the case, then when dogs and humans co-evolved, dogs were more likely to recognize and understand anxiety when it was triggered by something associated with a human. But this is, of course, pure speculation.

What is certain, however, is that dogs licking the air and licking their lips in social situations can be a sign of feeling worried or anxious.

If you often find your dog licking its lips without an obvious threat and food around, it may be necessary to investigate the cause further; it may be that the dog is in an environment that makes it feel uneasy, or it may even be a health problem such as nausea or oral discomfort. When the situation is uncertain, it is recommended that the dog be checked out at a veterinary hospital for your dog's health!