My two black kitty's (the others are light) have scabs on their chins. I don't know how long they have had this condition but I have washed the areas and applied a topical antibiotic repeatedly however it appears to do nothing. I do not observe them scratching the area more than usual but as a precaution, I applied Advantage to everyone. This is a multiple cat household and the others are light colored and not affected by this syndrome. What could this be? I have never seen this before.