Dog Diarrhea: Causes and When to Worry
Diarrhea is one of the most common reasons dog owners reach out to a vet — and also one of the most common things that resolves on its own within a day. The difference usually comes down to how long it lasts, what else is going on, and your dog's age.
Common causes
- A sudden change in diet, or a new treat
- Dietary indiscretion — eating something they shouldn't have on a walk
- Stress (boarding, travel, a new environment)
- Mild intestinal parasites
- A short-lived viral or bacterial infection
When it's likely more serious
- Diarrhea lasting more than 24–48 hours
- Blood in the stool, or stool that looks black and tarry
- Diarrhea combined with vomiting, lethargy, or fever
- Significant weight loss over time with recurring diarrhea
- Any diarrhea in a young puppy, especially unvaccinated ones (risk of parvovirus)
Watch for dehydration
Diarrhea's biggest real danger — especially in puppies, small dogs, and seniors — is dehydration. Signs include dry or tacky gums, loss of skin elasticity (gently lift the skin at the scruff; it should snap back quickly), sunken eyes, and lethargy. Any of these, combined with diarrhea, is a reason to call a vet rather than wait it out.
What's usually okay to monitor
A single episode of soft stool in a dog who is eating, drinking, and acting completely normal otherwise. Keep an eye on whether it resolves within a day; if it continues into a second day or worsens, it's time to call.
If you're trying to decide whether to wait it out or call the vet, PetCare can help you organize what you've observed — how long it's been going on, what else your dog is showing — and give you an urgency assessment as a starting point. It's not a substitute for an exam or a stool test.
This guide is for general information only and is not a substitute for professional veterinary advice, diagnosis, or treatment. If your pet is showing severe symptoms, contact a veterinarian or emergency animal hospital right away.