My cats chin is all red, like its lost some hair and its red and irritated, what is it?

My Rudy is 2 years old healthy cat who is allergic to generic foods so he eats hyoalergenic from soldans. I got him some treats from soldans and hes had about 5 so far, is that enough to cause an allergic reaction? I think it was dumb of me to get him treats since hes allergic but i guess i didnt think treats fell into that category. Do you think its the treats thats causing his chin to do this? It doesnt seem to hurt him too much as he can still clean himself fine and touch his body to his chin and lick without any pain. He is also a strictly indoor cat!