Why does a cat scratch constantly causing scabs and loss of hair and is there a home remed?

The cat may have fleas. Check by collecting some scurf from its coat on a piece of white paper. Dampen the scurf slightly, if any of it turns reddish, the cat has fleas. I don't know of a home remedy. Ask in the drugstore or, better still, ask a vet. If it's not fleas the cat might have ringworm. This needs professional treatment. Skin allergy to flea faeces may be the cause of persistent scratching which can result in bleeding and the formation of scabs. A good quality tubed-ointment type flea-killer applied once per month to the nape of the neck has been known to effect an almost overnight cure from this very distressing condition.