Hello...
Hmmm....as with any description their can be a small list/host of reasons.
Does your cat eat out of a metal, ceramic or plastic bowl? If the answer is plastic... it's possible he's become allergic to the die in the plastic bowl, you may notice some hair loss as well around mouth area.
sometimes cats get what's called feline acne and you can simply use wash cloth in warm water and place a small amount of mild soap on cloth and wipe affected area's a few times a day for about 1 week.
you can try that and if it does not help then I would have you take him to see the vet even call the vet on the phone and ask if he/she would help over the phone first any treatments you could try at home before bringing him for a exam
I hope that I have helped you.
Regards,
Barry
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