VetInfo explains that stomach upset is the most common reason that dogs throw up white foam. Dogs also vomit white foam for more serious reasons, such as rabies, kennel cough, stomach ulcers or inflammatory bowel diseases.
Vetinfo states that vomiting due to stomach upset is generally curable without veterinary treatment. However, pet owners should take the dog to a veterinarian if the vomiting is pervasive. Bilious vomiting syndrome typically causes the dog to start vomiting right after awakening. One way that a pet owner can solve this problem is by feeding the dog certain types of bland foods that help reduce the dog's stomach acidity overnight.
Bloat is another more serious cause of dogs vomiting white foam, according to VetInfo. Bloat can obstruct the veins that surround the stomach and lead to fatal complications, making it necessary to seek veterinary attention immediately. When a dog has this condition, its abdomen feels drum-like and appears bloated.
A number of symptoms of kennel cough manifest in dogs that have picked up the respiratory disease from other dogs. An infected dog experiences a dry cough and displays flu or cold-like symptoms. The disease also tends to cause dogs to cough up white foam.
Although white foam is commonly associated with rabies, it only appears in the late stages of the disease. Dogs with rabies display foaming of the mouth only after other symptoms, such as severe aggression.