When your pet is sick, it’s natural to worry about what may be the cause behind the symptoms. When your dog has diarrhea, the problem is unpleasant for both your pet AND for you. While some dog diarrhea causes may warrant a trip to the vet, some are less serious and will pass in a day or two.

Common Dog Diarrhea Causes

Change in Diet

If you have changed the food that you feed your dog, this could cause loose stools. This is especially true if you changed the food suddenly, rather than making a gradual transition from one food to another. This doesn’’t necessarily mean that the new food is bad for your dog, but rather that the sudden change has caused an upset in the digestive tract of your pet. It’’s best, when switching foods, to first mix some of the new food in with the old and then gradually increase the new food while decreasing the old food. This makes for a smoother transition and can help eliminate the problem.

Moldy Food and Water

Would you eat food or water that has been sitting out for 2 or more days? Probably not, but some pet owners expect their dogs to eat food and drink water that has been out for a week or more. Some molds can grow very quickly and cause diarrhea. You should change your pet’’s water at least once a day and food should not be left out for more than a day.

Intestinal Worms/Parasites

Not all worms and parasites cause diarrhea, but there some, such as Giardia, that do. It is caused when they disrupt the lining in the small intestine. Coccidia, which are especially common in puppies, are another parasite that can irritate the intestines and cause diarrhea. The lack of visible worms in the stool does not rule out parasite or intestinal worms as the cause of your pets symptoms. Treatment by a vet may be required.

Ingestion of Poisons

Insecticides and other household chemicals can be toxic to your pet. Diarrhea is just one possible effect of your pet ingesting such toxins. If you suspect that this is the cause of your pet’’s diarrhea, it’’s vital that you get him to a vet or call the pet poison control center right away. Because many household chemicals can be fatal if ingested by your pet, it’’s important to keep them out of reach in order to keep your pets safe.


If your vet has prescribed an antibiotic for your pet, this could be the cause of his diarrhea. Just as some humans experience side effects when taking certain medications, so do pets. If you suspect that your dog is experiencing side effects from prescribed medication, talk to your vet right away. He may tell you to continue the treatment, or he may prescribe a different medication. Do not discontinue administering the antibiotic without talking to your vet as he may decide that the side effect of having diarrhea is necessary in order to treat the problem for which he prescribed the antibiotic.


When a dog has pancreatitis, it causes an inflammation of the pancreatic gland. The disease can be the result of trauma, ingestions of toxins, a virus or other causes. The disease, for which diarrhea is just one symptom, is potentially life-threatening and treatment by a vet is required.

Ingestion of Certain Foods (such as chocolate)

Most pet owners know that dogs should not eat chocolate. In fact, eating the sweet treat that humans enjoy so much can be fatal to dogs. If your dog has ingested chocolate and has diarrhea, it’’s a good idea to call your vet. There are other foods that can cause similar symptoms. Chocolate and other harmful or unfamiliar food are a common cause of diarrhea in pets.

Ingestion of Foreign Objects

Most pet owners have seen their dog munching on grass one minute and vomiting the next. When a dog ingests a foreign matter, be it grass, a strange plant or a stuffed animal, his digestive system may not be pleased. The result can be vomiting and/or diarrhea. It should be clear when this is the cause as the offending object is likely to be visible in the stool or vomit.


One very common dog diarrhea cause is stress. If your dog has been boarded, left alone for longer than usual, been to the vet, experienced a move or an addition to the family (either two-legged or four-legged) this can cause stress in your pet. In some dogs, stress can trigger episodes of diarrhea. Usually, the symptoms will go away once the pet is removed from the stressful environment or he grows accustomed to the changes that have taken place around him.You do not necessarily need to run to the vet because your dog had one or two loose bowel movements. There are times, however, when an immediate trip the vet or pet emergency center is warranted.

Sudden Onset

When diarrhea comes on very suddenly, that alone may mean you need to see a vet. Dehydration is a serious complication, and this is especially true in puppies and in senior dogs. Dehydration has the potential to be fatal, so if the symptoms come on suddenly and are severe, you should get to your local vet or pet emergency center as soon as possible.

Bloody Diarrhea

If you see bloody diarrhea, contact your animal care doctor immediately. Waiting even a day or two could prove fatal to your pet.

Diarrhea Accompanied by Other Symptoms

If your dog has diarrhea but is otherwise acting normal, there may not be cause for alarm. If however, there are other symptoms such as lethargy, complete lack of interest in food or water or if the animal seems to be in pain, you need to contact your vet immediately.

The above list of dog diarrhea causes is not exhaustive, but it includes some of the most common. If you are worried about what may be causing your pet’’s symptoms, the best thing you can do is talk to your vet. It will help put your mind at ease and rule out any serious causes.


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