I remember the first time I found that my cat had diarrhea, I was terrified-is he sick? Can I help him? I had no idea what to do. If this is you, then you can relax. Cats get diarrhea for a variety of reasons. Often it is simply something they ate and is not a problem at all. After finding the first diarrhea, pay attention to the cat's next few bowel movements. If the diarrhea only occurred the one time, then it is likely that your cat ate something he shouldn't have, and will now be fine. However, if the cat continues to have diarrhea, then you may need to intervene.
One of the primary things that you should do is trying to prevent diarrhea. Cats, especially kittens, will eat anything off of the floor. My cat likes to eat my yarn when I knit. Try to keep stuff off of the floor. Make sure that your cat cannot access any human foods. Do not give your cat cow's milk-if you have been, stop immediately. Cats cannot process cow's milk and this will give them stomach problems, including diarrhea.
One common reason for stomach problems in cats is food intolerance. Check the type of food that you are giving your cat. Make sure it is high quality and have no food dyes. Food dyes, like those used in cat foods like Meow Mix can cause stomach issues. Switch out the food to something high quality, maybe even wet food. Do it slowly. A rapid food switch can also cause intestinal distress.
If you want, some vets will recommend a short-term switch to a bland, home-cooked diet. You may wish to try this with your cat. It usually includes cooked hamburger meat and white rice mixed together. You may wish to ask your vet whether he recommends this or other home cooked foods for your cats. You should not do this long-term as cats need nutrition that they cannot get from the meat we get at the store.
If it is not a food problem, then there may be an illness which is causing your cat's diarrhea. Stress, Intestinal Parasites, Hyperthyroidism and Feline Immunodeficiency Virus are all causes of diarrhea. You should bring your cat to the vet to check for these if he does not get better with a change in diet.
When your cat is suffering from diarrhea, you will need to watch him closely to make sure he doesn't get dehydrated. Most cats don't drink much, and the diarrhea will be pulling water out of their system. You might want to try wet food, as cats can absorb more water this way.