Diarrhea is loose, watery stools three or more times a day. It may be acute, persistent, or chronic. Diarrhea is never fun for our dog or us.
Healthy dog stools should be chocolate brown in color, log-shaped, firm, and clearly segmented. However, a dog's stool can be hard and dry or watery with no texture. Knowing what your dog’s stool typically looks like is essential so you can detect any changes. If there is a sudden change in your dog's stool, it may be a sign that the GI tract is upset and could be a warning of an upcoming bout of diarrhea.
Potential Causes of Diarrhea
• Ingestion of Appropriate or Inappropriate Items –Did you change something you give your dog as food or a treat? Did you change its water? If so, that might have been the cause of their loose stool. Even doing something like changing the amount of food can cause diarrhea. Also, dogs are incredible scavengers and live by the credo “Eat it now!”. Things they might consume include animal carcasses, garbage, feces, really, almost anything, including inedible items like toys, rocks, shoes, etc. Something like chocolate, grapes, raisins, and more can be toxic to dogs and cause diarrhea. If there is a possibility that your dog ate something in this category, you need to immediately call your veterinarian or the Animal Poison Control Center (888-426-4435).
• Food Sensitivities – Some dogs may react to certain foods, which typically cause skin issues but can also cause diarrhea.
• Stress
When under stress, the body releases hormones and neurochemicals that may cause diarrhea. Stressors for a dog can be fireworks, thunderstorms, and other loud noises, dehydration or the consumption of excess water, and physical injuries such as being hit by a car or a severe fall. Emotional stressors such as being left alone or in a new environment, such as with a pet sitter or boarding kennel, can also trigger diarrhea.
• Excessive Exercise
Physical exercise certainly has its benefits, but when taken to excess or in a hostile environment such as high heat and humidity, it can change the blood flow to the GI tract, triggering acute diarrhea.
• Pathogens
Various intestinal parasites, bacteria, and viruses can cause diarrhea. Your dog may pick these up from something he ate or in the water he drinks. If you keep up with your dog's regular treatment for worms, he will be protected from some but not all of these pathogens.
• Medication Side Effects
Antibiotics and other medications can cause diarrhea as they can kill the beneficial flora in your dog's gut microbiome.
• Inflammatory Bowel Disease (IBD)
Just like humans, our dogs can have inflammatory bowel disease. This is typically a chronic condition lasting for three works or more due to a chronic inflammation of the GI tract. It may also be called chronic enteropathy (CE). The latest research suggests dogs fed fresh food instead of ultra-processed food (kibble) are less likely to develop CE. Treatment of IBD or CE by your veterinarian will be essential.
• Other Medical Issues
Diseases of the liver, pancreas, and kidneys can cause diarrhea, as can hormonal imbalances and some cancers.
• Lack of Variety in Diet
Feeding your dog the same brand and formula of food day after day may negatively affect his gut microbiome, causing it to be less robust. Dogs fed a varied diet will often be less susceptible to diarrhea and other disorders of the GI tract.
Treatment of Diarrhea (from The Forever Dog, by Dr. Karen Becker)
Pro Tip: A dollop of canned 100 percent pumpkin (or fresh, steamed pumpkin, if you can get it) on food helps firm up soft stools and eases the dietary transition for many dogs (about one teaspoon for every ten pounds). Alternatively, slippery elm powder from your local health food store works wonders for soft stools if you find you’ve transitioned too fast or your dog’s snack causes loose bowels. We call this nature’s Pepto-Bismol. If your dog has diarrhea, activated charcoal (also from your health food store) to the rescue! One capsule for every twenty-five pounds of body weight usually does the trick. Wait until stools are 100 percent normal before introducing more
new foods. 
Don Hanson lives in Bangor, Maine, where he is the co-owner of the Green Acres Kennel Shop (greenacreskennel.com) and the founder of ForceFreePets.com, an online educational resource for people with dogs and cats. He is a Professional Canine Behavior Consultant (PCBC-A) accredited by the Pet Professional Accreditation Board (PPAB)and a Bach Foundation Registered Animal Practitioner (BFRAP). Don is a member of thePet Professional Guild (PPG), where he serves on the Board of Directors and Steering Committee and chairs the Advocacy Committee. He is also a founding director of Pet Advocacy International (PIAI). In addition, Don produces and co-hosts The Woof Meow Showpodcast, available at http://bit.ly/WfMwPodcasts/,the Apple Podcast app, and Don's blog: www.words-woofs-meows.com.The opinions in this post are those of Don Hanson.