Why is My Dog Vomiting White Phlegm?

From time to time, your dog may vomit up white phlegm or foam. Sometimes this white substance is composed chiefly of mucus, but at other times, it may be mixed with bile and food from the dog's small intestines. A variety of medical conditions can cause dogs to vomit mucus, including several serious diseases, so it is important to observe your dog carefully and consult your veterinarian if he vomits white phlegm.

Pug at the Doctor
Veterinary care is often required to determine the cause of vomiting white phlegm.
credit: bernardbodo/iStock/Getty Images

Blockage and Bloat

Bloat is a serious disease that can cause dogs to vomit phlegm, mucus and foam. Other symptoms of bloat include anxiety, abdominal pain and an expanded, rigid abdomen. Bloat occurs when a dog's stomach is unable to expel food or gas trapped inside. This can occur because of an intestinal obstruction, but it also occurs when a dog's stomach twists along its axis, thus preventing food and gas from entering or leaving the stomach. In some cases, portions of the stomach or intestines become deprived of blood and begin to die very quickly.

It Is Rarely Rabies

A dog with a foamy mouth or who produces white vomit containing phlegm may be exhibiting signs of rabies. Usually this manifests as excessive drooling, but it may accompany seizures or difficulty swallowing, making the symptoms appear similar to rabies. Nevertheless, these symptoms usually occur in the late stages of the disease, alongside other symptoms, such as aggression, self-mutilation and cerebral dysfunction.

Hemorrhagic Gastroenteritis

Sometimes, dogs who vomit phlegm are suffering from hemorrhagic gastroenteritis. Primarily characterized by bloody vomit and diarrhea, hemorrhagic gastroenteritis also can cause dogs to vomit phlegm. A serious and sometimes fatal condition, little is known about the cause and nature of hemorrhagic gastroenteritis. Diagnosis is often accomplished via the process of elimination, after all other common causes are ruled out. With treatment, many dogs recover, but it is important to seek prompt veterinary assistance.

Bilious Vomiting Syndrome

Bilious vomiting syndrome is a condition in which dogs regularly vomit a small quantity of bile and phlegm. This usually occurs in the morning or late at night, and is most commonly associated with dogs who are fed only once per day. Bilious vomiting syndrome is often easy to treat by simply splitting the dog's single, large meal into two or more smaller meals. This keeps the dog's digestive system full, and prevents frequent vomiting. Nevertheless, always consult with your veterinarian if you suspect that he may be suffering from bilious vomiting syndrome.

Other Possible Causes

In addition to gastritis, a condition in which the dog's stomach becomes inflamed, some diseases that are not directly related to the digestive system also may cause dogs to vomit white phlegm. Pancreatitis and kidney failure are two such examples, and both require prompt veterinary attention. This is especially important if other symptoms accompany the vomiting, such as fever, depression or pain.