Quick answer: Bad breath in cats is most commonly caused by dental disease — tartar buildup, gingivitis, or tooth resorption — but can also indicate kidney disease or diabetes.
Over 70% of cats over 3 have some form of dental disease. Tartar buildup causes bacterial overgrowth that produces sulfur compounds — the source of the bad smell. Yellow or brown buildup on the teeth and red or inflamed gums alongside bad breath almost certainly indicate dental disease.
A sweet or fruity breath odor can indicate diabetes. An ammonia or urine-like smell may indicate kidney disease — the kidneys fail to filter urea from the blood, which is then exhaled. Both are serious conditions that require prompt vet evaluation, especially in cats over 7.
Have your vet assess your cat's teeth at the next checkup — or sooner if the smell is strong or recent. Professional dental cleaning under anesthesia treats existing disease. At home, dental treats, water additives, and gradual toothbrushing introduction slow tartar buildup between professional cleanings.
Bad breath in cats is never normal and always has a cause. Dental disease is the most common and most treatable — early treatment prevents significant pain and tooth loss.