For example, a sudden switch from one cat food to another can result in a bout of diarrhea. We recommend introducing new food into your cat's regular diet a little bit at a time, making a gradual switch over a period of a couple of weeks. Cow's milk and related dairy products can cause diarrhea in some kittens and cats. This reaction is lactose intolerance. It occurs when an animal lacks sufficient amounts of an essential enzyme that facilitates digestion of cow's milk.
Cats can also develop an intolerance to other dietary ingredients, resulting in diarrhea.
By process of elimination, determine what is causing the reaction and cut it out of your cat's diet. The diarrhea should then clear up. It if doesn't, look for a cause other than dietary intolerance. One of the most common foreign bodies cats ingest is their own fur. Hairballs, or trichobezoars, are made up of loose fur, which the cat swallows as it grooms.