Dogs lick their lips and jowls for a range of reasons, some mundane and some that signify behavioral or medical issues that require veterinary attention. Pay attention to what else is going on and how often Fido is licking to determine what's really going on here, then seek treatment if it is appropriate.
Under stress, dogs often lick their lips and jowls. Dogs with nervousness, fear or anxiety also display this behavior. If your pet tends to lick his jowls in a certain situation, he's trying to communicate that it causes one of these negative emotions. Unusual sounds, places, people or animals can upset your pet, as can changes to his environment or confusing signals from people. Try to eliminate the stressor to help your pet feel better.
Dogs in a submissive state known as active submission or submissive fearful often lick the air or their face and jowl. Other signs of submission include whimpering, keeping the head and tail down, keeping the ears back and avoiding eye contact or making only brief eye contact. These dogs also may lick at other dogs' faces to indicate their submission. Get your dog to a space where he feels safe to reduce licking.
If this is a new behavior for your pet and is accompanied by lip smacking, teeth chattering, tooth grinding or face rubbing, it may indicate that your dog has oral discomfort such as dental pain or mouth sores. Nausea causes dogs to lick their faces and other surfaces. Other symptoms of nausea include drooling, dry heaving, excessive chewing and vomiting. If your pet has been nauseous for just a couple of hours, the sickness may pass. If it has been longer, see a vet to make sure there is no underlying medical condition.
Dogs can suffer from compulsive behaviors, so if your dog constantly licks his jowls it may stem from an anxiety- or stress-induced compulsion. If you pet's water dish has been empty all day, he may be dehydrated and thus licking. If your pet just finished a snack, he may be licking in hopes of finding stray crumbs.