Should my chihuahua be balding if he has dry skin or could it be something worse?

this started from a little scratch from our cat! & has gotten worse. I put ointment on him & it seems to work, but now he's getting them in places where he has no scratches. if anyone is , or has had similar experiences with this I'd love to know what the best treatment would be to try before I take pepe to the vet.