Just like humans, dogs experience physical decline as they grow older.
But when an old dog develops constant diarrhea, it can indicate anything from dietary changes to serious underlying medical issues that need immediate attention.
We outline why constant diarrhea in older dogs happens, what conditions may be causing it, and when you should be concerned. You’ll also learn what you can do to help your senior dog feel better and restore their digestive health.
Old Dog with Constant Diarrhea: Why It Happens
Constant diarrhea in an old dog often signals underlying health issues related to aging. As dogs grow older, their digestive system becomes more sensitive and less efficient, making them more prone to gastrointestinal disturbances.
Common causes include chronic conditions such as inflammatory bowel disease (IBD), pancreatitis, liver or kidney dysfunction, dietary intolerances, parasites, infections, cancer, or even side effects from long-term medications.
Older dogs also have weakened immune systems, which makes it harder for them to recover quickly from digestive upset. If your senior dog is experiencing ongoing diarrhea, it’s essential to consult a veterinarian to determine the root cause and provide appropriate treatment.
Common Causes of Constant Diarrhea in Old Dogs
1. Age-Related Digestive Changes
As dogs get older, their ability to digest and absorb nutrients weakens. An aging digestive system can become more sensitive to changes in diet, food ingredients, or fat content.
These changes may result in an old dog with constant diarrhea as their stomach and intestines become less efficient at processing food.
Additionally, the muscles of the gastrointestinal tract lose strength with age, making digestion slower and more prone to imbalances that lead to loose stools.
Related: Senior dog diarrhea and panting (Here’s why)
2. Dietary Sensitivities or Sudden Diet Changes
One of the most common reasons for constant diarrhea in an old dog is a diet that no longer agrees with their system.
Even if your dog has eaten the same food for years, aging can trigger new intolerances or allergies to ingredients like grains, chicken, or additives.
Old dogs are also more vulnerable to diarrhea when their food is changed suddenly.
Whether it’s switching from dry kibble to wet food or trying a new brand, abrupt dietary shifts can upset their stomach and lead to chronic loose stools.
Related: Old dog diarrhea and not eating (Here’s why)
3. Inflammatory Bowel Disease (IBD)
Inflammatory bowel disease is a frequent culprit behind an old dog with constant diarrhea.
IBD occurs when the intestines become inflamed, which disrupts normal absorption of nutrients and causes chronic diarrhea, weight loss, and sometimes vomiting.
This condition is common in senior dogs and often requires long-term management through medication and dietary changes.
4. Pancreatic Insufficiency
Exocrine Pancreatic Insufficiency (EPI) is a condition where the pancreas fails to produce enough digestive enzymes.
In senior dogs, this can manifest as constant diarrhea, greasy stools, excessive hunger, and weight loss.
Without those enzymes, food isn’t properly broken down, leading to chronic gastrointestinal issues.
EPI can be diagnosed with a blood test and typically requires enzyme replacement therapy for life.
5. Chronic Kidney or Liver Disease
Old dogs often suffer from organ dysfunction, especially involving the kidneys or liver.
Both organs play a critical role in filtering waste and supporting digestion.
When the liver or kidneys begin to fail, toxins build up in the blood and affect digestion, potentially causing your dog to experience frequent diarrhea.
These conditions also tend to show other symptoms like vomiting, appetite loss, increased thirst, or behavioral changes.
6. Parasites or Bacterial Infections
Even senior dogs can be affected by intestinal parasites like giardia, hookworms, or whipworms.
Constant diarrhea in an old dog may be due to these microscopic pests irritating the intestinal lining.
Bacterial infections such as salmonella or clostridium can also lead to ongoing diarrhea, especially if the dog has a weakened immune system due to age or illness.
7. Cancer or Tumors in the GI Tract
Sadly, cancer is more common in older dogs, and tumors in the intestines or stomach can cause constant diarrhea.
These growths can interfere with digestion and may be accompanied by weight loss, blood in stool, vomiting, or general weakness.
GI tumors are often diagnosed through imaging tests like ultrasound or X-rays, followed by a biopsy.
8. Medication Side Effects
Older dogs are often on one or more medications to manage arthritis, heart disease, or other age-related conditions.
Some of these drugs can cause gastrointestinal upset as a side effect, leading to persistent diarrhea.
Non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics are especially known for irritating the GI tract.
Always consult with your vet if you suspect your dog’s meds are causing diarrhea.
9. Stress and Anxiety in Senior Dogs
Just like humans, old dogs can become more sensitive to environmental or emotional stress.
Changes in routine, loss of a companion, loud noises, or visits to the vet can all lead to digestive issues.
Chronic anxiety can upset the gut-brain axis and lead to constant diarrhea in an old dog, especially if the dog is already vulnerable due to age.
What to Do If Your Old Dog Has Constant Diarrhea
If you’re dealing with an old dog’s constant diarrhea, taking the right steps early on is crucial. Here’s what you can do:
1. Monitor Symptoms Closely
Keep a daily log of your dog’s bowel movements — their frequency, texture, color, and presence of any mucus or blood.
Also note changes in appetite, thirst, energy levels, or vomiting.
This information will help your vet make a more accurate diagnosis.
2. Transition to a Bland Diet Temporarily
A temporary bland diet of boiled chicken and white rice (with no seasoning) can soothe your dog’s stomach.
Feed small, frequent meals and see if the diarrhea improves within 24–48 hours.
Avoid treats, table scraps, or fatty foods during this period, as they can worsen symptoms.
3. Make Any Diet Changes Gradually
If your vet recommends a change in food (such as switching to a hypoallergenic or easily digestible formula), do it gradually over 7–10 days.
Mix the old and new food in increasing ratios to help the digestive system adjust.
4. Check for Dehydration
Chronic diarrhea can quickly dehydrate a senior dog.
Check for dry gums, sunken eyes, skin tenting (if you gently pull the skin, it takes time to snap back), and lethargy.
Always ensure fresh, clean water is available.
You may also add an electrolyte solution to their water if approved by your vet.
5. Visit Your Veterinarian Promptly
If your dog’s diarrhea persists for more than 48 hours, worsens, or is accompanied by blood, vomiting, or weight loss, see a veterinarian immediately.
Older dogs don’t bounce back as quickly and can deteriorate faster than younger pets.
Your vet may perform fecal tests, blood work, ultrasounds, or x-rays to determine the root cause.
Treatments may include medications, prescription diets, probiotics, or other supportive care based on the diagnosis.
When to Seek Emergency Care for an Old Dog with Constant Diarrhea
Sometimes, constant diarrhea in senior dogs points to an urgent medical issue.
Seek emergency veterinary attention if:
The diarrhea is bloody or black (tarry)
Your dog is vomiting repeatedly
There are signs of dehydration
Your dog seems lethargic or unresponsive
They are also experiencing pain, bloating, or collapse
Prompt action can be lifesaving, especially in senior pets whose organs are more fragile.
Key Takeaway
Old dog constant diarrhea is not just a nuisance — it’s a symptom of an underlying problem that deserves careful attention.
Whether the cause is dietary, inflammatory, parasitic, or related to organ dysfunction, your senior dog’s health can improve dramatically with early intervention.
Remember aging dogs require a tailored approach to health and nutrition.
With the right care, dietary adjustments, and medical treatment when needed, you can help your senior companion enjoy their golden years in greater comfort and vitality.
Always consult your vet if you’re in doubt — better safe than sorry when it comes to our loyal best friends.