But is is only on one side of his body. He has no rash. He is on revolution and his diet is organic because if I give him store bought brands, he throws it up. He is 3 lbs overweight though because he is an indoor cat and exericse is not his regiment. He does run with his female companion. He is sterilized and other than the hair loss on his side starting a few weeks ago, he seems fine. He just had a check up in June and had his teeth cleaned, so he does see a vet regularly. Any ideas please?
Ringworm (a fungal skin infection that has nothing to do with worms!) can certainly cause hair loss. It's more common in cats that don't have a good immune system like kittens, chemotherapy patients, cats with Feline Immunodeficiency Virus (FIV - like HIV in humans), etc. Other possible causes are hypersensitivities (similar to allergies), skin parasites, trauma, etc., etc. Your veterinarian should be able to differentiate between the different causes and prescribe the proper treatment.
Drew Weigner, DVM, ABVP The Cat Doctor Board Certified in Feline Practice