Nice exhaustive article on a cat having bad breath.
A cat’s bad breath is often a clear indication that and perhaps may mean that a serious medical condition exists.
In order to find out the reason your cat has bad breath, your veterinarian is the best person to pinpoint the cause. A physical examination may reveal the cause of your cat’s problem. If not, further tests will likely be recommended. Be ready to answer questions about your cat’s diet, oral hygiene, exercise habits and general attitude and behavior.
kytkattin -- this sounds like it might be a conceivable cause. Does stress cause bad breath?? i've never heard of that! We live in a childless apartment with no other pets, but about 6 weeks ago we got new neighbours upstairs with two cats and i think this might be bugging him, as he's been a little more vocal and clingy since they moved in. But, on the other hand, his bad breath has been there for months, since well before these new neighbours moved in, so i don't know that this is the cause either.
Those are all very helpful indicators of what is causing bad breath.
Why Does My Dog or Cat Have Bad Breath? Ron Hines, DVM
Halitosis (bad breath) is a dental condition that affects not only humans, but cats as well. Cats are not expected to have odor-free breath, but breath with an unpleasant odor should raise concern. If your cat's breath gives off an extremely strong odor, it should be checked for possible underlying health problems. Cat bad breath, also known as halitosis is a condition that may occur due to food that gets stuck in between your pet’s teeth or may also be caused by an internal disease. Cat treats can prevent and eliminate the bad breath. However, if the problem is internal, this should be solved to eliminate the halitosis.Cat bad breath may be caused by various factors such as dentalproblems, tumors in the mouth cavity or gastrointestinal problems. The gastrointestinal tract may be affected by different conditions (such as infections, intestinal blockage, stomach tumors or stomach ulcers) whichwill cause the halitosis in your pet.Feline halitosis is a foul odor of the pet’s breath. The bad breath may be caused by different factors including an inappropriate diet, a dental problem, gingivitis or an internal problem. You may administer a few cat chew treats to eliminate the bad breath; these treats can give freshness to the breath.