Bad breath in cats is usually a sign of a problem, most often with the mouth (teeth and gums), but sometimes with internal organs like the kidneys, liver, or pancreas. It is not considered “normal cat smell,” so persistent or suddenly worse odor is a reason to contact a vet, especially if your cat seems off in any other way.

Quick Scoop

Your cat’s breath smells bad because something is creating extra bacteria, inflammation, or abnormal chemicals in or around the mouth, or in the body. Common issues range from dental disease and infected teeth to serious illnesses like kidney disease or diabetes, so a veterinary exam is important if the smell is strong or new.

Most common causes

  • Dental disease (top cause)
    • Plaque and tartar build up on the teeth, leading to gingivitis and periodontal disease that make the breath smell sour, rotten, or “swampy.”
* Infected or abscessed teeth can cause especially foul, almost decaying odors and pain when eating.
  • Oral infections, injuries, or foreign objects
    • Ulcers, stomatitis (severe inflammation in the mouth), or wounds can smell bad because of infection and dead tissue.
* A bit of bone, string, or other object stuck in the mouth or between teeth can rot or get infected and cause very smelly breath.
  • Diet and “gross snacks”
    • Some cats eat strong‑smelling food, garbage, or prey, which can leave lingering odors on the breath.
* Food stuck around teeth feeds mouth bacteria, which then release smelly compounds.

When the smell hints at bigger problems

Certain breath odors can point to internal disease as well as mouth issues.

  • Ammonia / urine‑like smell
    • Can be a sign of chronic kidney disease as waste products build up in the blood.
  • Sweet or fruity smell
    • Can occur with diabetes and a complication called ketoacidosis, which is an emergency.
  • Poop‑like / very fecal odor
    • May be linked to severe vomiting, gastrointestinal obstruction, or gut disease and needs urgent care.
  • Rotten, bloody, or ulcer smell plus drooling or difficulty eating
    • Can be caused by severe dental disease, deep infection, or even mouth tumors.

What you should do now

  • Book a vet visit soon
    • Any strong, persistent, or suddenly worse bad breath deserves a physical and oral exam to rule out dental disease, infection, or organ problems.
* Go urgently (same day or emergency) if you see signs like not eating, vomiting, heavy drooling, pawing at the mouth, weight loss, lethargy, or very unusual odor (ammonia, very sweet, or feces‑like).
  • At home, before the appointment
    • Check (gently) for red, swollen gums, visible brown tartar, loose or broken teeth, or anything stuck in the mouth if your cat allows it.
* Note any other changes (drinking more, peeing more, losing weight, hiding, vomiting) to tell your vet, since these help narrow down the cause.

Longer‑term fixes and prevention

  • Professional dental care
    • Regular dental cleanings under anesthesia are the main way to treat and prevent dental disease and chronic bad breath.
* Your vet may recommend extractions or treatment for oral inflammation if needed.
  • Home dental habits (only after vet approval)
    • Daily or frequent toothbrushing with cat‑safe toothpaste can greatly reduce plaque and smell.
* Dental diets, chews, or water additives approved for cats can help but should not replace vet care.

If your cat’s breath is bad enough that you notice it often, assume it is a medical clue, not just a quirk, and let a vet check what’s going on.

TL;DR: “Why does my cats breath smell so bad?” Most likely because of dental disease or an oral problem, but in some cases the odor can signal serious internal illness, so a vet exam is the safest next step.

Information gathered from public forums or data available on the internet and portrayed here.