My one-year-old cat has developed a flakiness on his chin. It is black and looks like dirt. It is similar to flea dirt but he does not have fleas or the flakiness on any other part of his body. It does not seem to bother him in any way other than he just looks dirty. I remember reading several years ago something about cats having allergies to their food dishes that were made of plastic. I use plastic dishes with mine. Do you think this could be the problem or something else?