Our Veterinary Team Explains Common Causes and When to Worry

At Scottsdale Veterinary Clinic, one of the most frequent questions we hear from concerned pet owners is: “Why does my dog have diarrhea?”

We completely understand how upsetting it can be to see your beloved dog feeling unwell. Diarrhea is messy, stinky, uncomfortable, and sometimes alarming. While many cases are mild and can be easily treated, others can indicate a more serious underlying issue that requires veterinary attention. In some cases (mostly in small puppies and toy breed dogs), if they experience diarrhea for even a short time, it can result in hypoglycemia (low blood sugar) that may result in needing an emergency vet visit. Dogs can have diarrhea with blood in it sometimes, which should be cause for alarm and to seek care from a veterinarian.

Our goal is to help you understand the most common causes of diarrhea in dogs, what signs to watch for, and when it’s time to bring your dog in for care.

1. Dietary Indiscretion (Eating Something They Shouldn’t)

Many dogs are curious by nature and love to investigate the world through their noses and mouths. Unfortunately, that sometimes means eating things they shouldn’t, such as table scraps, garbage, spoiled food, or something they picked up outside.

This is often referred to as “garbage gut” and is one of the top reasons dogs experience temporary digestive upset and diarrhea.

What you might notice:

  • Loose or watery stool
  • Possible vomiting
  • Otherwise acting playful and normal

In mild cases, diarrhea can resolve with a bland diet (such as boiled chicken and rice) and plenty of fresh water. However, if symptoms last more than a day or two, or if your dog seems uncomfortable or has other concerning symptoms, we recommend giving our clinic a call.

2. Sudden Changes in Diet

Switching your dog’s food too quickly - even to a healthier or higher-quality option - can upset their digestive system. Dogs need time to adjust to new foods because their gut bacteria require time to adapt. To avoid digestive upset, we recommend gradually transitioning to new food over 7–10 days by mixing increasing amounts of the new food with the old.

3. Parasites

Intestinal parasites such as roundworms, hookworms, giardia, or coccidia can cause diarrhea, especially in puppies, newly adopted dogs, or dogs that spend time in dog parks, daycares, or kennels. Some of these parasites can even be transmitted to people, so early diagnosis and treatment are important.

Our clinic can perform a fecal ova and parasite test to quickly check for parasites and recommend the right treatment to help your dog recover. Parasites that go untreated can lead to more severe concerns, such as nutritional deficiencies and anemia.

4. Infections: Bacterial or Viral

Just like humans, dogs can suffer from infections that cause diarrhea. Infectious diarrhea is often accompanied by other symptoms like vomiting, fever, lethargy, or loss of appetite. If your dog is showing any of these signs, please contact us immediately (especially in young puppies), where dehydration and complications can escalate quickly.

These infections may include:

  • Parvovirus (especially dangerous in puppies and unvaccinated dogs)
  • Distemper Virus
  • Bacterial infections like Salmonella or Campylobacter
  • Clostridium overgrowth
  • Anaplasmosis (tick-borne infection)

5. Food Intolerances and Allergies

Some dogs have sensitive stomachs or allergies to specific ingredients such as chicken, beef, grains, or dairy. In these cases, diarrhea may be chronic or recurrent, and you might also notice:

  • Skin irritation
  • Ear infections
  • Itchy paws or face

Our team can help guide you through an elimination diet trial or recommend a prescription hypoallergenic diet to identify the source of the problem and bring your dog relief.

6. Stress and Anxiety

Yes, dogs can get diarrhea from stress too! Just like humans who get an upset stomach before a big event, dogs can develop stress colitis when they’re anxious. Stress-related diarrhea is usually temporary, but we can suggest strategies, calming aids, or medications if needed to help manage your dog’s stress levels.

Common triggers include:

  • Boarding, Doggy Day Care, and Pet Resorts
  • Separation Anxiety from being left alone
  • Moving homes or changes in routine
  • Loud noises (like fireworks)
  • Travel

7. Chronic Conditions and Inflammatory Diseases

If your dog has frequent or ongoing diarrhea, vomiting, or weight loss, we may recommend further diagnostic testing such as bloodwork, imaging, or biopsies to get to the root of the issue.

Sometimes diarrhea is a sign of a more chronic or serious underlying condition such as:

  • Inflammatory Bowel Disease (IBD)
  • Pancreatitis
  • Liver or kidney disease, Renal failure, or Liver shunts
  • Chronic Idiopathic Hepatitis
  • Endocrine disorders like Addison’s disease
  • Immune Mediated Thrombocytopenia
  • Cancer

8. Foreign Body Ingestion or Toxin Ingestion

Diarrhea can be a sign of a Foreign Body, which occurs when pets ingest items like string, clothing, sticks, toys, or any other item that will not readily pass through their gastrointestinal tract, including human food products such as bones or trash.

Some ingested items, such as older pennies or lead material, can cause systemic toxicities, while others may cause regional damage to the intestinal tract itself due to compression or obstruction. Gastrointestinal foreign bodies, especially strings, can often lead to perforation of the intestinal tract. While some small foreign bodies will pass, many will become lodged along the gastrointestinal tract and cause discomfort and make your pet sick. Surgical intervention is not always required with gastrointestinal foreign bodies, however, most gastrointestinal foreign bodies become lodged within the stomach or intestines and require surgery such as a gastrotomy (opening the stomach) or enterotomy (opening the intestine).

Other items that dogs frequently ingest that cause severe toxicity and diarrhea include:

  • Toxic Plants such as Oleander or Sago Palm
  • Marijuana or Vape Pens
  • Chocolate, especially the darker chocolate varieties
  • Xylitol (found in sugar free gum, sugar free peanut butter, and many other foods)
  • Grapes or Raisins
  • Bufo Toads Secretion (Marine Toad or Sonoran Desert Toad)

9. Allergic Reactions to Vaccines or Medications

Allergic reactions to vaccines or medications can sometimes cause diarrhea in dogs, though it’s usually accompanied by other symptoms. These may include vomiting, lethargy, facial swelling, hives, or intense itching. While mild digestive upset can occur on its own, true allergic reactions tend to trigger a more systemic response. If your dog shows any combination of these signs after receiving a vaccine or new medication, contact your veterinarian right away.

10. Parvovirus & Distemper (Common in Puppies)

Canine Parvo is a highly contagious virus that attacks the gastrointestinal tract and can cause symptoms of bloody diarrhea, vomiting, fever, lethargy, loss of appetite, and can quickly become fatal. It can resemble other diseases including distemper, bacterial infections, foreign body, Giardia etc. Parvo is extremely contagious to other dogs and can be spread by direct dog-to-dog contact and contact with contaminated stool, environments, or people. This virus can be preventable with routine vaccinations, but is not treated by them. Even with treatment, your dog may not survive this viral infection, however hospitalized care for canine parvovirus greatly increases survival chances.

Canine distemper is a contagious and serious disease caused by a virus that attacks the respiratory, gastrointestinal and nervous systems of puppies and dogs. All dogs are at risk, but puppies younger than four months old and dogs that have not been vaccinated against canine distemper are at increased risk of acquiring the disease. Initially, infected dogs with distemper will develop watery to pus-like discharge from their eyes. They then develop fever, nasal discharge, coughing, lethargy, reduced appetite, diarrhea and vomiting. As the virus attacks the nervous system, infected dogs develop circling behavior, head tilt, muscle twitches, convulsions with jaw chewing movements and salivation (“chewing gum fits”), seizures, and partial or complete paralysis. Distemper is often fatal, and dogs that survive usually have permanent, irreparable nervous system damage. The virus can also be found in wildlife such as foxes, wolves, coyotes, raccoons, skunks, mink and ferrets and has been reported in lions, tigers, leopards and other wild cats as well as seals.

When Should You Call the Vet?

We know it can be hard to decide when to wait and when to seek help. Even if you’re unsure, our team is always here to offer advice and help you decide whether your dog needs to come in for care.

Here are some clear signs that it’s time to call our clinic:

  • Diarrhea lasting longer than 24 hours, or call sooner if any additional systems below
  • Blood in the stool (bright red or black and tarry)
  • Vomiting in addition to diarrhea
  • Lethargy, weakness, or signs of pain
  • Refusing to eat or drink

What Diagnostics Can Help Determine the Cause of My Dog’s Diarrhea?

  • Fecal Analysis for Ova & Parasite Screening
  • Giardia Testing
  • Parvo Testing
  • Fecal PCR
  • Complete Blood Count & Chemistry Panel
  • Bile Acids Testing or Liver Biopsy
  • X-rays
  • Ultrasound
  • Anaplasma or Lyme Disease Testing
  • Distemper PCR Testing

How We Can Help With Diarrhea Treatment Options

At Scottsdale Veterinary Clinic, we understand that your dog is a beloved part of your family. Whether it’s a simple upset stomach or something more complex, we’re here to provide compassionate, thorough care to help your pet get back on their paws.

From diagnostic testing to nutritional guidance and treatment options, we’re your partner in keeping your dog healthy and happy.

Some treatments that may be needed after diagnosing the cause of your dog’s diarrhea are:

  • IV Fluids for hydration
  • Deworming treatment, such as Panacur or Drontal
  • Parvo Treatment and Hospitalization
  • Withholding food for a period of time
  • Bland Diet (e.g., Chicken and Rice, Prescription Diets)
  • Nutritional Supplements and Vitamins
  • Probiotics (e.g., Fortiflora)
  • Antibiotic or Antifungal Therapy

If you have questions or concerns about your dog’s diarrhea, don’t hesitate to give us a call. We’re happy to help.