Ok, so maybe it's not the most appealing topic to discuss, but Ringworm is a very real issue to consider whether you have just one cat, or many. Many health issues are not passed between cats and humans, but ringworm can be, and the cycle can be ongoing unless treated.
There are no "worms" in ringworm. Ringworm is spread via fungal spores. They can affect the skin,hair, and claws. Initially, cats may not show signs of the disease, but they are still contagious. As it progresses, you may notice a rash, circular bald spots, scaly or crusty skin, stubbly hair, altered hair color, dandruff, and excessive grooming.
When the hair falls off the cat's body, the fungal spores will be spread. Other animals, AND PEOPLE, can become infected. Animals and people with immune deficiencies are much more susceptible.
It's a myth that you can easily rid your house of ringworm. The spores can float in the air and drop anywhere...carpet, tiles, the couch...anywhere.
If left untreated, a cat's case of ringworm probably will eventually go away, but it could take 9 months to a year. And your cat is uncomfortable in the process, so it's not ideal to just assume it will go away. And, you may catch it as well. It could continue to cycle between you and your pet/pets indefinitely unless treated. Veternanrians typically treat cats with both an inexpensive oral medication and some topical ointment. the shortest course of treatment takes ~45 days, but many cases take considerably longer.
Bottom line, if you notice any changes in your cat's skin or hair, consult a veterinarian right away. Keep an eye on your skin too!
**Information obtained from the January 2013 issue of CatWatch.