I had a cat with a ringworm twice in my life and twice I tried home remedy for that and it worked like miracle. All you need is raw potato and regular salt. Peel potato, make a hole inside and fill it with salt. Place potato on the plate and let it sit and release juice. Then apply this juice as often as you can to the place where you or your cat has ringworm and it's going to disappear in a few days. In my case it took me 2 days to get rid of that ringworm in my cats.