Why Does My Dog Have Diarrhea? Causes, Warning Signs and What to Do

By Dr Duncan Houston

Quick Answer

Dog diarrhea is commonly caused by diet changes, infections, parasites, stress, or underlying disease. Mild cases may resolve with simple care, but persistent diarrhea, blood in stool, or signs of illness require veterinary attention.

As a veterinarian, I treat diarrhea as a symptom, not a diagnosis, because it can range from a simple stomach upset to a sign of serious gastrointestinal or systemic disease.

It happens quickly.

One moment your dog is completely fine, and the next you are dealing with loose stool or full-blown diarrhea. While it is very common, it should not always be ignored.

The key is knowing when it is mild and when it is something more serious.

Types of Diarrhea in Dogs

The appearance of your dog’s stool can give useful clues.

Soft or Poorly Formed Stool

Often linked to:

• Mild dietary changes

• Stress

• Temporary gut upset

This is usually less urgent but should still be monitored.

Watery Diarrhea

More severe and can lead to dehydration quickly.

Common with:

• Infections

• Dietary indiscretion

• Toxins

This is more concerning, especially in small or vulnerable dogs.

Mucus in Stool

Often associated with inflammation of the large intestine.

Common causes include:

• Colitis

• Stress

• Dietary sensitivity

Bloody Diarrhea

Always needs attention.

• Fresh red blood suggests lower intestinal irritation

• Dark, tarry stool suggests digested blood and is more serious

Common Causes of Dog Diarrhea

Dietary Indiscretion

One of the most common causes.

This includes:

• Eating garbage

• Sudden diet changes

• Table scraps

• Foreign material

Parasites

Intestinal parasites can cause diarrhea, especially in younger dogs.

Examples include:

• Worms

• Giardia

• Other protozoa

Infections

Bacterial, viral, or protozoal infections can affect the gut.

Puppies are particularly at risk of more severe disease.

Food Sensitivity or Allergy

Some dogs react poorly to certain ingredients.

This can cause:

• Chronic or recurring diarrhea

• Soft stools

• Gastrointestinal discomfort

Stress or Anxiety

Stress can affect gut function.

Triggers may include:

• Travel

• Boarding

• Environmental changes

Chronic Disease

Ongoing or recurrent diarrhea may be linked to:

• Pancreatitis

• Liver disease

• Inflammatory bowel disease

• Other systemic illness

Toxins or Medications

Certain substances can irritate the gastrointestinal tract.

Examples include:

• Human foods or toxins

• Some medications such as NSAIDs or antibiotics

When to See a Vet

You should seek veterinary care if:

• Diarrhea lasts more than 24 to 48 hours

• There is blood in the stool

• Your dog is lethargic

• There is vomiting or loss of appetite

• Your dog cannot keep fluids down

• Your dog is a puppy, senior, or has other health conditions

• You suspect toxin exposure

Diarrhea combined with other symptoms is always more concerning.

What You Can Do at Home

For mild cases in an otherwise bright dog:

Short Rest for the Gut

• Skip one or two meals if appropriate

• Do not restrict access to water

Feed a Bland Diet

• Small, frequent meals

• Easily digestible food

• Gradual return to normal diet once improved

Maintain Hydration

• Ensure access to fresh water

• Monitor for signs of dehydration

Monitor Closely

Watch for:

• Frequency of diarrhea

• Changes in energy

• Appetite changes

• Presence of blood

If anything worsens, seek veterinary care.

What Not to Do

• Do not give human medications

• Do not delay treatment if symptoms persist

• Do not fast young or vulnerable dogs for extended periods

• Do not assume it will resolve if signs are worsening

What Your Vet May Do

If your dog needs treatment, your vet may recommend:

Physical Examination

Assess hydration, abdominal pain, and overall condition.

Fecal Testing

Check for parasites or infectious causes.

Blood Tests

Evaluate organ function and systemic health.

Imaging

Used if obstruction or more serious disease is suspected.

Treatment Options

Treatment depends on the cause.

It may include:

• Anti-diarrheal medications

• Fluid therapy

• Gastrointestinal support

• Parasite treatment

• Dietary management

• More advanced care in severe cases

When It Is an Emergency

Seek urgent veterinary care if your dog:

• Has severe or continuous diarrhea

• Has large amounts of blood in stool

• Is weak, collapsed, or very lethargic

• Cannot keep fluids down

• Shows signs of dehydration

• Is very young, small, or already unwell

Final Thoughts

Diarrhea is common, but it is not always harmless.

Most mild cases improve quickly, but persistent, severe, or unusual diarrhea should always be taken seriously. Looking at the whole picture, not just the stool, is the most important part.

FAQs

How long can a dog have diarrhea before it is serious?
More than 24 to 48 hours, or sooner if there are other symptoms, should be checked.

Can I give my dog pumpkin?
Plain pumpkin can help in some mild cases, but it is not a cure for underlying problems.

What is the difference between diarrhea and soft stool?
Diarrhea is watery and unformed. Soft stool still has some shape but is not fully firm.

If your dog develops diarrhea, tracking frequency, appearance, and any associated symptoms can help identify patterns early. The ASK A VET™ app can help you monitor these changes and decide when further care is needed.