Q. My cat has been scratching on his neck a lot (he's got fleas) and a month ago we found a patch that was raw and hairless now we found 2 more help?
DR. CHRISTIE LONG, D.V.M., C.V.A.
A. It's very possible that your cat has developed allergies to flea saliva. It's pretty common in cats that have been routinely infested with fleas. Unfortunately dealing with it at this point is not as simple as getting the fleas off (and making them stay away); you have to deal with the allergies themselves. That's likely what's behind the hair loss and the constant scratching.
Your vet can help to get rid of the fleas, and then use medications to treat the allergies. Other things that need to be ruled out are mites (mange) and ringworm, as well as food allergies, but I'd bet the fleas are the underlying problem.