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Why does my pet have diarrhoea?

Symptom: Diarrhoea

Diarrhoea is a common issue in pets and can happen for many reasons, from changes in diet to underlying health conditions. In this article, we’ll explain what different types of diarrhoea can look like, common causes of diarrhoea in pets, what you can do at home to help, and when it’s important to seek veterinary advice. 


Written by Dr. Mariella Roberts, Veterinary Surgeon, Animal Trust Vets CIC | Published July 2025 | Review date July 2027 | This advice is for UK pets only and is not a replacement for seeing a vet

Symptom: Diarrhoea

Signs my pet may have diarrhoea

  • Loose or watery stools: the stool will be softer and less formed than usual and may be difficult to pick up. 

  • Increased frequency: your pet may need to go to the toilet more often than usual.  

  • Mucus or blood: you may notice mucus, which can appear like slime/jelly, or blood in the stool, which can range from red to a black colour. 

  • Accidents in the house: if your pet is normally well house-trained, they may start having accidents in the house. 

  • Behavioural changes: your pet may seem less active, lethargic, or off their food. 

Why does my pet have diarrhoea?

  • Dietary indiscretion, such as scavenging or eating food outside of their normal diet, e.g. table scraps

  • A sudden change in diet, for example switching their normal food without a transitioning period

  • Infection (viral/bacterial/parasitic), related reading Lungworms 

  • Inflammatory/allergic, related reading Food Allergies 

  • Reaction to medication

DOs - My pet has diarrhoea, what to do at home

  • In acute cases of diarrhoea a highly digestible low-fat diet, preferably wet food, that contains a protein source that has been eaten before.  

  • In chronic cases, a dietary trial consisting of a specific (hydrolysed) diet and strictly only that, at least for the first 2-3 months may help to reduce the problem (if related to dietary intolerance/allergy), but this should only be done in conjunction with your veterinary surgeon, and after ruling out more urgent issues. 

  • Probiotics: these beneficial bacteria may help to restore the gut's natural balance. 

  • Hydration: diarrhoea can lead to dehydration, so it's crucial to provide plenty of water and possibly an electrolyte solution. 

DON'Ts - My pet has diarrhoea, what not to do at home

  • Don't give rich or fatty foods 

  • Don't give human medications 

  • Don't give table scraps  

  • Don’t make abrupt dietary changes 

  • Don't give dairy products  

When should I think about going to the vet if my pet has diarrhoea?

Most cases are self-limiting and resolve rapidly, however, if your pet's diarrhoea lasts longer than 24-48 hours, if they seem unwell, with other symptoms like vomiting or lethargy, or if you see any blood in their stool, then it would be advisable to contact us.

When is it an emergency if my pet has diarrhoea?

  • Severe, unrelenting vomiting and diarrhoea 

  • If your pet is very young 

  • Extreme lethargy or weakness 

  • Repeated vomiting 

  • Suspected toxin or foreign body ingestion