Why is my dog throwing up foam?

Vomiting in dogs is often confused with (A) regurgitation of food, which may be covered in mucus, and (B) expectoration = coughing up mucus.

Dogs vomit white foam for many reasons, including infectious disease, eating strange things, and going too long between meals. If your dog solely vomits foam or a yellow or clear liquid, it could indicate acute gastritis, pancreatitis (brought on by eating items that are not recommended), intestinal blockage, or other issues. The most common cause of vomiting white foam is some type of stomach upset. It will often occur if your dog drank water too quickly after exercising or ate something that disagreed with him, such as grass or an inedible substance. If the vomiting continues, visit your veterinarian to make sure your dog hasn't swallowed something that he can't digest. A dog may suffer from bilious vomiting syndrome, which usually occurs soon after the dog wakes up (caused by too much acid in the dog's stomach and is more common in dogs with digestive problems). If it happens regularly, your dog may have an ulcer or inflammatory bowel disease and may need medical treatment. However, it can often be cured with 12 hours of fasting or a couple meals of boiled chicken and rice. Your dog also may need to have a bland bedtime snack to coat his stomach and reduce acid while sleeping.

White foam is one of the characteristic symptoms of bloat, which is the swelling of the stomach that causes it to rotate, trapping the stomach's contents in the stomach and obstructing veins around the stomach. This can quickly lead to death if not treated, so it should be addressed immediately. Additional symptoms include unsuccessful attempts to vomit, pacing, anxiety, restlessness, attempts to hide, desire to go outside at odd times, a hunched up appearance, bloated abdomen that feels like a drum and refusal to sit or lie down.

Dogs will often cough up a yellow mucous or white foam when suffering from kennel cough, an upper respiratory disease contracted from other dogs. The most common symptom of kennel cough is a dry hacking cough. Additional symptoms include eye and nasal discharge, fever, lethargy and loss of appetite. Para-influenza or other colds, may also cause your dog to vomit white foam, and will include other cold-like symptoms, such as eye and nasal discharge, sneezing and fever. Vomiting white foam is a rabies symptom. The foaming of the mouth characteristic of rabies is caused by nerve damage to the mouth and throat that prevents the dog from swallowing.

Illnesses that can cause vomiting include hepatitis, pancreatitis, diabetes, and kidney disease. If the vomiting persists a few days, even with a bland diet, consult your veterinarian. (source credit vetinfo.com)