Hi - I found this article on cat scatching the chin:
Dirty Chins
You may notice that your cat has a dirty chin - little black spots that look like acne. Simply put, it IS acne. And it can be quite painful, so you should take steps to get it cured as soon as possible. Though you might want to check with your vet, who can provide you with some medicine, you might want to try this first: Clean the area with hydrogen peroxide (pour some on a clean white washcloth, and sponge off the chin). You'll probably need to do this twice a day for a week or so.
Next, take a look at the food dishes: how often do you clean them? Are they plastic? Are they very deep? Cat food dishes should be cleaned on a daily basis, particularly if you are feeding canned food. Plastic dishes may aggravate the acne, and deep food bowls definitely will. (Ours eat out of glass custard dishes.)
http://www.xmission.com/~emailbox/tips.htm
and this:
Feline Acne
Cats can develop acne just as humans do. Usually it is only on the chin. It will appear as small black spots. The reasons for feline acne are as complex as it is for humans. Sometimes a food allergy (such as chocolate with humans or milk with cats) can cause it or sometimes the cat does not clean its chin properly.
Tips on caring for feline acne
It is important to keep food dishes clean. Acne has bacteria associated with it. The cat's chin comes in contact with the edge of the food/water bowl, leaving bacteria. The next time the cat uses the bowl, it can come in contact with this bacteria and spread it on the chin.
Use glass or metal food/water dishes. It is next to impossible to remove the bacteria from acne from plastic dishes.
Wash the food and water dishes daily. This removes the bacteria from the dishes and helps to keep the problem from getting worse. Also, in multi-cat households, it will help reduce the chance of others breaking out with it.
Bathe the cat's chin daily with a disinfectant soap/solution from the vet. Nolvasan, Xenodine, Betadine soaps are a few of the ones to try. More severe cases may need to be washed twice a day. DO NOT USE HUMAN ACNE SOLUTIONS. These are too strong for cats and may cause serious problems. Don't try to pick the spots off, just clean it well.
Visit the vet if you can't get the acne to clear up within a week or two, or if the acne is severe or infected. The vet may prescribe antibiotics or other acne treatments for these cats.
Once the acne is cleared up, keep an eye out for reoccurrences. Washing the cat's chin once a week is a good preventative measure.
http://fanciers.com/cat-faqs/health-care.shtml
There were other articles. I searched "cat scratching chin."
Maybe the cleaning the bowl thing will work - good luck.
