The most common cause of diarrhea in dogs is food intolerance, often relating to the ingestion of something outside of the animal's regular diet. Toxic plants, spoiled foods and inedible items, such as toys or socks are often the reason for short bouts of dog diarrhea, according to WebMD.
A change in a dog's normal diet or an intolerance to a particular food can also cause loose, watery stools. Many cases of diarrhea occur after a dog eats leftovers or table scraps, and is especially common during the holidays, states Healthy Pets by Mercola. Dogs may experience diarrhea when switching to a new brand of food, although low-grade pet foods may cause chronic diarrhea in some animals.
Bacterial or viral infections, parasites, and certain diseases can cause diarrhea in dogs as well. Diarrhea may be a symptom of kidney disease, liver disease, colitis, inflammatory bowel disease or cancer of the digestive tract and may require medical attention. In most cases, dogs recover from diarrhea within 24 hours without treatment. Pet owners should contact their veterinarian if their dog is excessively lethargic, vomiting or experiencing diarrhea for more than a day, recommends WebMD. Bloody or dark-colored stools could indicate internal bleeding and require immediate medical attention.