Make it a point to check your cat's ears periodically. Grooming time is a good time to do this. Look for a change in color inside the ears. Just like the gums and inside of the mouth, a yellowish or bluish cast to the skin on the inside of your cat's ears can be a sign of a major health problem; alert your veterinarian right away.
Cats do a pretty good job of keeping their ears clean. Outside of some normal wax, then, you shouldn't see much in your cat's ears. Any sort of inflammation, raw skin, or crustiness is a tip that something's amiss. Debris in a cat's ear -- it usually looks like dirt or coffee grounds -- is an indication of ear mites, tiny insects that live and breed in the ear canal. Itchiness is another sign of ear mites, but not all cats with ear mites will scratch or rub at their ears -- and not all cats who scratch or rub their ears have ear mites.
Cats that go outdoors need to have their ears inspected from time to time for other reasons. In cold weather, frostbite is a real danger. Those nice, tall, pointy feline ears are made up mostly of skin and cartilage. There isn't a lot of blood flow to the ears. Even being caught outside for an hour when the temperature takes a sudden drop can be enough for the tips of your cat's ears to freeze.
Outdoor (or indoor/outdoor) cats are also more likely to get into scrapes with other cats. The ears are easy targets for scratches and bites during even the mildest of cat fights. A cat's small, sharp teeth can make a puncture wound that seals up immediately, trapping dirt and germs inside and causing infection. The cat may look and act all right when he comes home, but a few days later an abscess -- a tender, swollen area of trapped pus -- may form, and the cat can run a fever. At this point, you'll need to take him or her to the vet.
"The eyes," goes the old saying, "are the windows of the soul." Shift your own eyeballs over to the next page to discover why, for cat owners, the eyes are also a window to how your cat is feeling.