There are lots of reasons why your cat has a persistent cough, depending on when he coughs and the type of cough. We'll look at just a few of the potential causes here, but ultimately your veterinarian is the person to make a definitive diagnosis.
If your cat coughs only when exercising, it may be acute bronchitis, a lung inflammation. Cats with chronic bronchitis are more likely to cough up mucus. Cats may also develop feline asthma, a chronic lung inflammation that can make breathing difficult. One symptom is a persistent cough, but it's usually accompanied by other symptoms such as wheezing, bluish gums, open-mouthed breathing and gasping for breath.
More serious diseases than asthma can start out with a simple cough. Congestive heart failure, for example, may begin with a mild, moist cough at night that becomes productive over time. Coughs may also be due to pneumonia, a fungal infection, lymphoma, heartworms and a host of other illnesses -- many of which can be successfully treated if caught early. That's why any cough that lasts for more than a day or two, or is accompanied by other symptoms, should be checked out by the vet just to be on the safe side.
If your cat is coughing and also pawing at his mouth or shaking his head, there may be something stuck in his throat or mouth. Open your cat's mouth -- taking care that you avoid being bitten -- and look inside. If you find a foreign body and can remove it easily, do so. Keep a close eye on your cat for the next few days to make sure that he doesn't develop an infection. If the object is stuck in the roof of the mouth, between the teeth or you can't locate it at all, see your vet right away.
A collar can sometimes cause a cat to cough, especially if it's too tight. A tight collar may cause a honking cough. If your cat wears a collar, check the size. You should be able to slip the tip of your finger between the collar and the cat's neck easily. Since cats like to squeeze into tight places, collars can pose a choking hazard. Many experts recommend you only use cat collars with elastic or breakaway features so that if the cat snags the collar on something, it'll come off easily.