Motion and Car Sickness
One surprising cause of drooling in dogs is motion or car sickness. You will notice your dog lick his lips excessively, accompanied by drooling. He may also whine, refuse to move, and vomit. In some cases, your dog may lose control of his bladder or bowels. Motion sickness can occur in any breed or age of dog. Stress can add to this; if your dog associates rides in the car with negative experiences (such as going to the vet for shots or other uncomfortable procedures), then he may develop a fear of riding in the car. This also adds a mental element to the physical discomfort your pet feels when riding in the car. However, medication exists to alleviate symptoms of motion sickness.
Mouth Disease or Tooth Decay
While drooling in most dogs is a good thing, helping to keep teeth healthy, excessive drooling is not. It can be a sign of gingivitis and periodontal disease. You will notice the gums becoming inflamed and sore. Without treatment, teeth will become loose and either fall out or fracture. If your dog has chipped a tooth (not related to periodontal disease), you will notice excessive drooling as a sign that something is amiss. Cuts, bruises, or other injuries to the mouth or gums may also result in drooling.
Even if you are running the air in your car, keep in mind that your furbaby wears a “fur” coat year-round and cannot sweat or cool off the way that you can. What is comfortable or even chilly to us may not quite cool off your dog on an especially hot summer day. Also, brachycephalic dogs such as Boston Terriers, Pugs, and Boxers have an even harder time properly panting in order to cool off their system, so if you notice your dog excessively drooling, be sure heat stroke is not an issue.
Excitement and Anxiety
As previously stated, car rides associated with going to the vet for shots or other unpleasant procedures can cause anxiety in your dog that can lead to excessive drooling. Intense emotions can cause your dog to drool excessively. Anxiety about traveling in the car can lead to this. On the other hand, your dog can be so happy about a ride in the car that he drools as a response as well. Your vet can help you with mild medications if necessary or give you some tips on conditioning your dog so that this is no longer a problem.
Other Possible Causes
Before considering other causes, it is imperative that you make sure your dog has not been exposed to rabies. Rabies causes foaming at the mouth and is usually accompanied by excessive thirst and other behavioral changes. Your dog may also have a foreign object lodged in its mouth or throat that is causing excessive saliva. Sometimes medication, allergies, or poisoning can cause drooling. Your dog may also suffer from congenital defects (some dogs are more prone to drooling, such as Bulldogs) or from defects in the way the mouth is formed that lead to excessive saliva production.