It could be if the skin is dry and scaly. It's a common fungal infection and highly contagious. Your vet can give you an antifungal cream. It's definitely worth taking your cat to the vet! There's lots of info about ringworm, just google it!
Fungal infection could be the cause. But a big issue with many cats with hair loss can result from stress or just allergies. Take it to the vet for a check up persay, and ask them about it. A simple blood test should reveal the reasoning
My cat lives outside and this winter he was gone for several days at a time. When he came back, his fur was thickly matted on both of his sides. (he was not fixed and was in search for females constantly). We finally took him to be fixed and asked the vet to shave him all over, but he just shaved the under side of him. Now his fur is coming out in gobs and he is still loosing his fur. Is this due to a "bug" or what! He never had this happen ever before. It looks like fur is trying to come in but not at a good rate and its very skimpy. Help! He looks like crap.