Cats can develop stinky breath for several reasons, with the most common being dental issues like plaque buildup, gingivitis, or tooth decay. Just like humans, cats need oral care, and without it, bacteria can accumulate, leading to bad breath. Another possibility is diet—certain foods or treats might contribute to the odor. If the smell is particularly foul or accompanied by other symptoms like drooling or loss of appetite, it could indicate a more serious condition like kidney disease or diabetes. A vet visit is a good idea to rule out health problems.